Applying Behavioral Theory to Increase Mindfulness Practice Among Adolescents : an Exploratory Intervention Study Using a Within-Trial RCT Design

ORIGINAL PAPER Applying Behavioral Theory to Increase Mindfulness Practice Among Adolescents: an Exploratory Intervention Study Using a Within-Trial RCT Design Marguerite Beattie 1 &Nelli Hankonen 1,2 &Gloria Salo 1 &Keegan Knittle 1 &Salla-Maarit Volanen 3,4 Published online: 9 July 2018 #The Author(s) 2018, corrected publication July/2018 Abstract For mindfulness programs to have sustained benefits, participants should continue to practice mindfulness independently. Behavioral theories have been used to predict and change other health behaviors, but have rarely been applied to mindfulness practice. This research aimed to identify predictors/determinants of sustained mindfulness practice after a school-based mindfulness program (Study 1) and to develop and test a booster intervention to increase mindfulness practice (Study 2). These studies were embedded in a larger trial evaluating a school-based mindfulness program involving 12–15 year-olds (Healthy Learning Mind, HLM). Study 1 examined theory-based predictors of mindfulness practice among participants in Batch 1 of the HLM trial (n= 310). These findings were used to develop a brief motivational booster intervention, which Study 2 evaluated in a within-trial cluster-randomized controlled trial in Batch 3 of the HLM trial (HLM Only arm n=177;HLM+boosterarmn= 152). In Study 1, 40% of youths reported having practiced mindfulness at a 6-month follow-up. The perception that peers were practicing mindfulness exercises predicted mindfulness practice (β=.497,p= .002), and a key self-reported reason for non-practice was that they did not find mindfulness useful. The booster intervention (designed to specifically target these descriptive norms and outcome expectations) demonstrated some positive trends in the determinants of mindfulness practice, but did not increase mindfulness practice. The limited effectiveness of the booster intervention might be explained by the minimal contact time of the booster intervention or its delivery in the later lessons of HLM. This study demonstrates how behavior change theories can be applied to help promote independent mindfulness practice outside of intervention settings. Keywords Determinants of mindfulness practice .Health behavior change .Behavioral theory .Theory of planned behavior . Reasoned action approach .School-based program Introduction Mindfulness programs have been developed and implemented in many different settings in recent years. Some mindfulness programs have been developed especially for youth, including several in school settings (Broderick and Metz 2009;Flooket al. 2010;Kuykenetal.2013). Schools are a potentially valuable environment for teaching mindfulness exercises, as they are far-reaching and can encourage beneficial habits for young people. A recent meta-analysis concluded that school-based mindfulness training improves cognitive variables, such as attention and learning, as well as psychological measures of stress, coping, and resilience (Zenner et al. 2014). While these programs seem to benefit young people, it is not clear whether in-class sessions alone are sufficient for students to obtain the full benefits of mindfulness practice. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12671-018-0976-2) contains supplementary material, which is available to authorized users. *Marguerite Beattie [email protected] 1 Faculty of Social Sciences, Social Psychology, University of Helsinki, PO Box 54, 00014 Helsinki, Finland 2 Faculty of Social Sciences, University of Tampere, Kalevankatu 4, 33014 Tampere, Finland 3 Folkhälsan Research Center, Topeliuksenkatu 20, 00250 Helsinki, Finland 4 Faculty of Medicine, Department of Public Health, University of Helsinki, Tukholmankatu 8 B, P.O. Box 20, 00014 Helsinki, Finland Mindfulness (2019) 10:312–324 https://doi.org/10.1007/s12671-018-0976-2 Among adults, more frequent home practice of mindfulness exercises is associated with improvements in mindfulness and well-being and decreases in psychological symptoms (Carmody and Baer 2008). Similar evidence exists among students and adolescent populations as well. For example, Kuyken et al. (2013) found that greater practice of mindfulness after a 9-week school-based mindfulness intervention was associated with better well-being and less stress 3 months later, and Huppert and Johnson (2010) observed positive associations between the time spent practicing mindfulness outside the classroom, improvement in psychological well-being, and the quality of mindfulness reported among adolescent boys. As regular mindfulness practice seems key to improving psychological functioning and well-being, facilitating sustained mindfulness practice may be a way to improve the effectiveness of mindfulness programs. There is little empirical evidence concerning which factors predict sustained mindfulness practice or how to best promote independent practice of mindfulness. There is the Liverpool Mindfulness Model, which hypothesizes that motivation, intention, positive expectations, and attitudes lead to mindfulness practice (Malinowski 2013). Other hypothesized predictors of mindfulness practice include certain open, Bmindful^ characteristics and positive attitudes towards mindfulness practice (Stanley et al. 2011), habits and self-control (Galla and Duckworth 2015), and action planning and commitment (Galla et al. 2016). Despite some investigation into these possible predictors of mindfulness practice, the determinants of other health-supporting behaviors have been more thoroughly investigated and may help to shed light on additional predictors of mindfulness practice. Accounting for and specifically targeting known theoretical determinants of a behavior can improve the effectiveness of interventions intended to change that behavior (Chatzisarantis and Hagger 2005; Hardeman et al. 2002; Riebl et al. 2015). One prominent theory in behavior change literature is the Theory of Planned Behavior (TPB; Ajzen 1991), which posits that attitudes (i.e., beliefs related to the consequences of the behavior and the evaluation of the importance of those outcomes), perceived norms (i.e., beliefs regarding what others think one should do), and perceived behavioral control (i.e., beliefs regarding one’s ability to effectively perform the behavior) predict one’s intention to perform a behavior, and that intention in turn explains behavioral performance. The reasoned action approach (RAA; Fishbein and Ajzen 2010), an extension of the TPB, incorporates additional theoretical constructs described later. Meta-analyses indicate that the TPB and RAA predict intention and behavior relatively well, both cross-sectionally and prospectively, in various populations (e.g., Armitage and Conner 2001; McEachan et al. 2011; Sheeran and Taylor 1999; Sheeran et al. 2016), and these theories have been used to predict a number of health behaviors, including physical activity, diet, screening behaviors, and condom use (Ajzen 2015;Albarracinetal.2001; Cooke and French 2008; Hagger et al. 2002; McEachan et al. 2011). When it comes to predicting mindfulness practice however, only some components of the RAA have previously been investigated. As mentioned earlier, Malinowski (2013)usedintention, expectations, and attitudes to predict mindfulness practice in his model, and Stanley et al. (2011) also tested attitudes toward the mindfulness training program as a predictor of mindfulness practice. The impacts of perceived behavioral control and perceived norms on mindfulness practice have not been previously investigated, although the RAA holds that they too are significant to the prediction of behavior. In the RAA, perceived norms were expanded to consist of not only injunctive norms (i.e., perceptions about what others think a person should do) as in the TPB but also descriptive norms (i.e., perceptions of what others are actually doing), which McEachan et al. (2016) have demonstrated to have substantial predictive power of intention to perform the behavior. Descriptive norms could be particularly important in explaining behavior among adolescents, where behavioral patterns are not fully developed and the perceived need for conformity is heightened (Knoll et al. 2015). Indeed, descriptive norms predict behavior better among younger samples than among older samples (Rivis and Sheeran 2003). As the frequency of independent mindfulness practice after school-based interventions predicts positive outcomes (Carmody and Baer 2008; Huppert and Johnson 2010; Kuyken et al. 2013), it is critical to implement school-based mindfulness programs that foster maintenance of mindfulness practice after these programs end. Applying behavioral theory to this problem (see Fig. 1) may lead to positive outcomes and increase rates of mindfulness practice. In this study, we take an approach that is commonly used in developing theory-based behavior change interventions in other domains (e.g., physical activity, diet). This includes using existing data to understand important theoretical predictors of a behavior (i.e., mindfulness practice) and subsequently using this understanding to develop an intervention that changes these predictors en route to changing behavior. The present paper describes two studies which were embedded within a larger trial of a school-based mindfulness intervention called healthy learning mind (HLM; Volanen et al. 2016,2018). HLM is a 9-week school-based mindfulness program delivered to adolescents aged 12–15. It is based on the B.b^(pronounced Bdot b^) program developed in the UK (Kuyken et al. 2013)and consists of classroom-based lessons covering different mindfulness techniques. HLM was tested in a large cluster-randomized controlled trial (cRCT) among 56 schools in southern Finland in order to examine its effects on mental well-being (e.g., resilience, depressive symptoms, and total difficulties), cognitive functions, psychophysiological responses, and academic achievement at post-treatment, 6-month, and 1-year follow-ups (Volanen et al. 2016,2018). The HLM trial was not conducted in all schools simultaneously, but rather over the course of four trial periods Mindfulness (2019) 10:312–324 313 (i.e., batches), which allowed for the analysis of one batch to inform the creation of a booster that was delivered in a subsequent batch. In this paper, Study 1 examines the utility of an extended RAA model to explain mindfulness practice and investigates students’self-reported reasons for non-practice in the first batch of the HLM cRCT. Based on this, a booster intervention was developed and implemented during the third batch of the HLM cRCT. Study 2 examines the feasibility of this booster intervention and explores its effects on students’intentions for mindfulness practice and mindfulness practice itself, in a small-scale within-trial cRCT within the third batch of the HLM study. See Fig. 2. Study 1 Method Participants The participants in Study 1 were 310 middle school students who received the HLM intervention during the first batch of the HLM trial. Participant characteristics are presented in Table 1. Procedure Within the HLM cRCT, 247 schools from Southern Finland were invited to participate, of which 56 accepted the invitation and enrolled in the study. After entering the study, schools were matched according to language used for teaching (i.e., Finnish, Swedish, or English), grade, and school location and were then randomly allocated to a mindfulness intervention group (85 total classes), an active control group (79 total classes), or a no-treatment group (28 total classes). Of the 10 schools that participated in the first batch of the HLM trial (spring 2014), analyzed here in study 1, five schools were allocated to the HLM program. Data were collected at baseline, at 5 weeks (intervention arm only), immediately after the 9-week intervention (via a feedback form), around 10 weeks from baseline, and 6 months after baseline from the adolescents, their parents, and teachers (Volanen et al. 2016,2018). This study uses data collected at 10 weeks and 6 months. See Fig. 3for a flow chart of Study 1. Fig. 1 Applying Ajzen’s and Fishbein’s theory to mindfulness practice Spring 2014: •HLM's 1st Batch February 2015: •HLM's 3rd Batch begins •Analysis of HLM's 1st Batch Spring 2015: March 2015: •Booster is designed April 2015: •Booster is administered Autumn 2015: •Data from Baseline and Ten Weeks available from the 3rd Batch •Evaluaon of the Booster Fig. 2 Timeline of present studies with reference to HLM 314 Mindfulness (2019) 10:312–324 Measures Outcome expectations were measured at 10 weeks with six items, each responded to on a five-point scale ranging from Btotally disagree^to Btotally agree.^The item stem was: BThe ability to relax and calm my mind when I’m stressed, nervous or anxious …,^which was followed by these items: B1. Can help me feel better,^B2. Can help me be healthier,^B3. Can help me learn,^B4. Can help me perform better (e.g., in sports),^B5. Does not help me in any way,^B6. Takes time from other important things.^The last two items were reversed-scored, and the mean of all items was taken as the score for outcome expectations. It should be noted that this measure (as well as the measure of self-efficacy for mindfulness practice) uses Bthe ability to relax and calm my mind^as a proxy for mindfulness exercises or practice, which limits conclusions drawn from this measure. Perceived norms were measured by three items, including descriptive and injunctive norms, on a five-point scale ranging from Btotally disagree^to Btotally agree^on the 10-week survey. Descriptive norms about peers’mindfulness practice were measured with the item: B1. My friends do some of the exercises we learned,^and injunctive norms with the average of the items: B2. My friends think that it’s OK that I do the home exercises,^and B3. My parents think that it’sOKtodo the exercises I have learned.^ Self-efficacy was measured by a mean of four items on a four-point scale ranging from BIamcertainIcannot^to BIam certain I can^on the 10-week survey. The question and item stems were: BI think I can calm my mind, even when …,^B1. I have an important test or speech in school,^B2. I’mstressedor in a bad mood,^B3. I have to perform in sports, music, etc. outside school,^and B4. I have quarreled with someone/some people who are close to me.^ Intention to practice mindfulness was assessed with a single item in the ten-week survey which read: BDuring the next months, I intend to use the exercises I have learned to relax and calm my mind.^Respondents answered on a seven-point scale ranging from Btotally disagree^to Btotally agree.^Due to a non-normal distribution, intention was categorized into those who disagreed with the intention statement and those who agreed or neither disagreed nor agreed. Frequency of mindfulness practice in the past month on the 6-month survey was assessed with four items describing exercises taught in the HLM curriculum. Participants responded to the stem, BThink about the past one month (four weeks) and answer the following questions. During the past one month I did the following exercises at home …^on a five-point scale ranging from Bnot once^to Balmost every day or every day.^The exercises were as followed: B1. Short breathing exercises that lasted under 10 minutes (e.g., breathing 7/11),^B2. Long breathing exercises that lasted over 10 minutes,^B3. Movement relaxation (e.g., the Move in the wind—exercise, walking mindfully),^and B4. Mindfulness in everyday tasks (eating, brushing teeth etc.).^A total frequency score was calculated by taking the mean of responses to these four items. As this variable was skewed, it was categorized into those who had not practiced at all and those who had practiced at least once. Self-reported reasons for not practicing mindfulness exercises were assessed at 6 months by asking respondents: BIf you have not done any mindfulness exercises during the past half year, what do you think are the reasons for this? Choose all that apply^:B1. I didn’t find them useful,^B2. The Table 1 Demographics of the intervention arm of HLM’s first batch First Batch Frequency Percentage Gender Girls 134 43 Boys 137 44 Missing 39 13 Mother tongue Finnish 258 83 Swedish 0 0 Other 13 4 Missing 39 13 Total 310 100 Fig. 3 Study 1’sflowchart Mindfulness (2019) 10:312–324 315 exercises were too difficult,^B3. I have forgotten to do the exercises,^B4. I have been too busy to do the exercises,^B5. I think the exercises are boring,^B6. I have not needed the exercises,^and B7. Other, please specify^(open-ended question). Data Analyses Two of the main variables under study were not normally distributed. Intention had a kurtosis score of −1.22 and a bimodal distribution, and practice at 6 months had a skewness score of 2.82 and a kurtosis score of 10.13. Due to the nonnormal distributions of intention and practice at 6 months (Field 2017;LeiandLomax2005), these variables were dichotomized into two groups using a median split. As selfefficacy, perceived norms, descriptive norms, and outcome expectations were distributed normally, they were not recoded and remained continuous. Consequently, logistic regression analyses examined the extents to which these predicted mindfulness practice at 6 months, using the recoded dichotomous intention and mindfulness practice variables. Results In the first batch of the HLM trial, 60% of the 310 students reported no mindfulness practice at the 6-month follow-up. The other 40% of students reported practicing mindfulness once or twice in the past month. Students’ages ranged from 12 to 15 (see Table 1for more demographic information). Overall, the reliability of the measures was good, with Cronbach’s alphas ranging from .88 to .67 (See Table 2). The most frequently reported reason for not practicing mindfulness was not finding mindfulness practice to be helpful (32% of participants; see Table 3). Neither outcome expectations (β=−.014, p= .943), injunctive norms (β=−.112, p= .894), self-efficacy (β= −.201, p= .408), nor intention (β=−.529, p= .116) predicted mindfulness practice. However, descriptive norms did (β= .497, p= .002). The model (Nagelkerke’sR 2 = .11) fit well (χ 2 (5) = 20.77, p= .001). Parametric regression analyses with non-dichotomized variables showed comparable results, except that in these analyses, intention did significantly predict mindfulness practice. Discussion To conclude, descriptive norms predicted mindfulness practice during the past month at the 6-month follow-up. Selfefficacy, outcome expectations, and intention, as operationalized here, did not predict mindfulness practice. However, another operationalization of outcome expectations, namely, students not finding the mindfulness exercises to be helpful, was the most frequently given reason for not practicing mindfulness. This pointed to the possibility that demonstrating the advantages and benefits of mindfulness practice in this population might help to improve outcome expectancies and therefore also increase mindfulness practice. Therefore, descriptive norms and outcome expectations (perceived helpfulness) were chosen as the targets for the booster intervention developed and tested in Study 2. Table 3 Frequencies and percentages of given reasons for non-practice in study 1 (N=213) Reason Frequency Percentage (%) Not helpful 100 32.3 Exercises too difficult 4 1.3 Forgot to do exercises 67 21.6 No time to do exercises 50 16.1 Exercises were boring 43 13.9 No need for exercises 66 21.3 Other reason 15 4.8 Note. Those who practiced would not have chosen a reason, but are still included in the percentages. This is not a percentage of only those who did not practice due the way in which the item was phrased Table 2 Means, standards deviations, and Cronbach’s alphas for study one’smeasures Measure Mean SD Range Cronbach’sα Use of mindfulness exercise to relax (baseline) 1.40 .58 3 N/A Lesson attendance 8.08 1.20 8 N/A Outcome expectations 3.59 .86 4 .875 Perceived norms 3.14 .86 4 .671 Descriptive norms 2.39 1.08 4 N/A Self-efficacy 2.96 .62 3 .847 Intention 3.41 1.90 6 N/A Practice at home (6 months) 1.32 .64 4 .869 Total sample N= 310. All variables measured at the 10-week survey (post-treatment) unless otherwise indicated. N/A = not applicable for single-item measures 316 Mindfulness (2019) 10:312–324 Study 2 Method Participants See Table 4for demographic information about the sample. Procedure The newly developed booster intervention was evaluated in a within-trial cRCT within the third batch of the main HLM cRCT and only included classes that had been allocated to receive the HLM intervention (k= 25). Classes allocated to the mindfulness treatment arm of the main HLM intervention were stratified by intervention provider and class size by the study coordinator of the HLM program. Subsequently, classes were block-randomized, using an online tool available from random.org, to be the comparison group and receive the mindfulness intervention alone (HLM Only; 12 classes containing 152 total students) or to receive a modified version of the mindfulness intervention, which included a booster intervention delivered during the eighth and ninth sessions (HLM + booster; 12 classes containing 177 total students). One class was excluded from intervention delivery because of low participation in intervention sessions. Other researchers were blinded from the randomization until after all analyses had been conducted, and student recipients were also blinded from randomization. Only data from the surveys at baseline and 10 weeks were available for this analysis. See Fig. 4for the flow chart. Based on the findings of Study 1, which revealed that descriptive norms and outcome expectations were the main predictors of mindfulness practice, a booster intervention was developed to be implemented during the last two sessions of the HLM intervention—this was due to time considerations, as the third batch of the main trial had already started. During the penultimate session (session 8), 5 min was available for the present booster intervention. It consisted of two parts: a slideshow presenting peer benefits and a motivational video showing peers’experience of mindfulness practice. The slideshow presentation displayed the percentages of peers who had experienced specific benefits after having practiced mindfulness at least once after the intervention: B79% have reported better concentration while in class,^B76% have reported better concentration in their hobbies,^B69% have reported managing stress better,^B77%havereportedcoping with difficult emotions (e.g., fear, aggression, anxiety) better,^ B79% have reported sleeping better,^B75% have reported getting better grades,^B84% have reported getting along betterwithfamilymembers,^and B85%havereportedgetting along better with friends.^This presentation targeted both descriptive norms (i.e., that they have peers who are practicing mindfulness) and perceived benefits of practicing mindfulness. The second part of session 8 was a video from Kelty Mental Health Resource Centre called (Kelty Mental Health 2013). The video presented peers (or adolescents slightly older) commenting on their own experiences of mindfulness practice and its benefits. In this way, both descriptive norms and perceived benefits were again targeted. This is also supported by another theory in another way: according to Self Determination Theory (SDT), people are more likely to adopt values and behaviors promoted by those to whom they feel connected and in whom they trust. Using peers to describe the benefits of mindfulness practice might thus have fostered students’need for relatedness and thus have helped to internalize the information and enhance their self-determination and motivation for mindfulness practice (Deci and Ryan 1985). During the last session (session 9), 10 min was available for the booster intervention, which consisted of two parts: the Identifying Personal Motives Group Activity (Hankonen et al. 2017) and a benefits and practice matching sheet. The card sorting activity was completed first in small groups of four to five students, and it targeted both descriptive norms (i.e., showing that students’peers intended to practice mindfulness) and perceived benefits (through discussing and sharing Table 4 Demographic information for study 2 HLM Only HLM + booster Frequency Percentage Frequency Percentage Gender Girls 89 50.3 59 38.8 Boys 64 41.8 64 42.1 Missing 24 13.6 29 19.1 Mother tongue Finnish 144 81.4 121 79.6 Swedish 0 0 1 0.7 Other 8 4.5 1 0.7 Missing 25 14.1 29 19.1 Total 177 100 152 100 Mindfulness (2019) 10:312–324 317 personally relevant benefits). After dividing into small groups, each group was given an identical set of cards, with each card naming a potential benefit of mindfulness practice. Cards were color-coded for different categories of benefits (i.e., focus, positive emotions, acceptance, life-management, relationships, and others). Students were asked to choose one to three cards that described the benefit(s) that they would like to obtain by practicing mindfulness. After choosing their cards, each group shared their choices with the rest of the class. This Identifying Personal Motives Group Activity has been used previously in the Let’s Move It intervention to promote physical activity among adolescents (Hankonen et al. 2017). The benefits and practice matching sheet (see supplementary materials) targeted perceived benefits by listing the known benefits of mindfulness practice and allowing the students to define their own goals and ways to achieve them. In this way, the benefits and practice matching sheet task also fostered students’ experience of autonomy, which, according to SDT, is a basic psychological need leading to self-determined motivation. The left side of the matching sheet contained boxes describing numerous potential benefits of mindfulness practice, which werecolor-codedinthesamewayasinthecardsortingactivity, while the right side of the sheet contained boxes that listed each of the mindfulness exercises that students had learned during the past 9 weeks as part of the mindfulness intervention. Students were instructed to choose one to two benefits they would like to receive by practicing mindfulness and to draw a line connecting each potential benefit with the mindfulness exercises they thought would most likely help them to achieve the chosen benefits (BifIwant’… ‘then I will do the following practice^). After making their selections and if-then plans, students were encouraged to take the sheet home and place it somewhere visible to remind them of their personal goals and plans. The benefits and practice sheet is an adaptation of the volitional help sheet (VHS), which is a tool designed to enhance the construction of effective implementation intentions (Armitage 2008). VHS has been used successfully in interventions targeting health behavior changes in smoking (Armitage 2008), drinking (Arden and Armitage 2012), and physical activity (Armitage and Arden 2010). See Table 5for a delineation Fig. 4 Study 2’sflowchart 318 Mindfulness (2019) 10:312–324 of the concepts behind the components of the booster intervention and Table 6for a description of the booster. Measures Most measures were the same as in Study 1, but there were some exceptions as described below. Outcome expectations were measured by a mean of the four items available at baseline and 10 weeks on a five-point scale ranging from Btotally disagree^to Btotally agree.^The item stem was: BWhat do you think about the following? The ability to relax and calm my mind when I’m stressed, nervous or anxious …^The items were as follows: B1. Can help me feel better,^B2. Can help me be healthier,^B3. Can help me learn,^and B4. Can help me perform better (e.g., in sports).^ The fifth and the sixth items used in Study 1 were only present in the 10-week survey, so they were omitted in Study 2. To assess their use of a mindfulness exercise to relax, participants were queried with the stem, BHow often do you do the following activities to relax?^and participants then responded to one item BI do a mindfulness exercise^ with possible responses of: BNotatall,^BSeldom,^ BSometimes,^and BOften.^ Motivation for learning to relax and calm one’smind was measured with a single item that read BI would like to learn to relax and calm my own mind better.^Responses were given on a five-point Likert scale ranging from Bdisagree^to Bagree.^Similar to outcome expectations and self-efficacy, this measure also did not explicitly state mindfulness practice as the object. Practice at home at 10 weeks (during the program) was used to operationalize the targeted behavior. Respondents were asked how often they practiced the mindfulness exercises at home, with the item stem BI practiced …^:B1. Counting breaths in one minute,^B2. …seated body-scan,^B3. Breathing 7–11,^B4. Beditation (body-scan),^B5. Mindful breathing (paying attention to sensations of breath),^B6. Mindful eating,^B7. .b (pausing and breathing),^B8. Walking mindfully,^B9. Watching thoughts pass by as if they were traffic,^B10.Seeing thoughts as clouds passing through the mind,^B11. Feeling my feet on the floor (when I feel stressed or anxious),^B12. Breathing relaxation (e.g., the balloonexercise),^B13. Relaxation through imagery (e.g., the beachexercise),^and B14. Movement relaxation (e.g., the move in the wind-exercise).^The six-point scale ranged from Bmany times aday^to Bnot once^and was reversed scored. These items were averaged into a mean practice-at-10-week score. Data Analyses Outcome expectations, use of a mindfulness exercise to relax, intention, and practice of mindfulness were non-normally distributed, and so changes and differences in these variables were assessed with non-parametric tests, in addition to parametric tests. Outcome expectations at baseline had a skewness score of −1.086 and a kurtosis score of 1.727. Use of a mindfulness exercise to relax at baseline had a skewness score of 1.179 and a kurtosis score of .84. Intention had a kurtosis score of −1.34 and a bimodal distribution. Practice at 6 months had a skewness score of 2.13 and a kurtosis score of 3.88. Finally, lesson participation had a skewness score of −1.48 and a kurtosis score of 3.23. These non-normally distributed variables were recoded into variables with two to three categories having relatively equal numbers of participants. Table 5 Booster activities, theoretical determinants, and associated behavior change techniques Session Booster intervention activities Targeted theoretical determinants Behavior change techniques 8➢PowerPoint presentation of data about peer practice and mindfulness benefits ➢Video of interviews with practicing peers explaining some mindfulness benefits ➢RAA: descriptive norms and outcome expectations ➢SDT: relatedness ➢5.1. Information about health consequences ➢5.3 Information about social consequences ➢5.6 Information about emotional consequences ➢6.1 Demonstration of the behavior ➢15.1 Verbal persuasion about capability ➢16.3. Vicarious consequences 9➢Mindfulness benefits discussed with cards in a group activity ➢Benefit and mindfulness exercise matching sheet ➢RAA: descriptive norms and outcome expectations ➢SDT: relatedness and autonomy ➢1.1 Goal setting (behavior) ➢1.3 Goal setting (outcome) ➢5.1. Information about health consequences ➢5.3. Information about social and environmental consequences ➢5.4. Information about emotional consequences ➢6.3. Information about others’ approval ➢13.2 Framing/reframing ➢5.2 Salience of consequences Note. The behavior change techniques are based on the behavior change technique taxonomy v1 by Michie et al. (2013) Mindfulness (2019) 10:312–324 319 Practice of mindfulness, use of a mindfulness exercise to relax, and intention were recoded into the presence or absence of any practice or intention. Outcome expectations were recoded into Btotally disagree^to Bneither agree nor disagree,^Bagree a little,^and Bagree.^Lesson participation was recoded into nine lessons, eight lessons, and less than eight lessons. Change scores were first calculated for retesting the mixed ANOVA variables before they were recoded. Independent samples ttests (for normally distributed variables), Mann-Whitney Utests, and chi-square tests were used to examine baseline differences between the HLM Only and HLM + booster groups. Within-group changes in outcomes were assessed using paired ttests for normally distributed variables, and Wilcoxon signedrank tests for non-normally distributed variables. Mixed within-between ANOVA tests were used to examine differences in trajectories between the HLM Only and HLM + booster groups over time in normally distributed variables for which both baseline and 10-week data were available. For non-normally distributed variables, change scores were calculated, the change scores were recoded into variables with two to three categories, and then analyzed in chi-square tests as in Study 1. Between-groups differences at 10 weeks were assessed using Mann-Whitney Utests for variables for which no baseline data were available. Results At baseline, there were no differences between the HLM Only and HLM + booster groups on outcome expectations (χ 2 (2, n= 170) = 1.26, p= .532), motivation to relax and calm one’s mind (t(263) = −.864, p= .385), or use of a mindfulness exercise to relax (U=8409,p= .475). There were also no differences between groups in their levels of lesson attendance within the HLM program (χ 2 (2, N= 258) = 1.18, p=.556). Within the HLM Only group from baseline to post-treatment, outcome expectations significantly decreased (Z=− 3.059, p= .002), use of a mindfulness exercise to relax significantly increased (Z=−3.059, p= .003), and motivation to relax and calm one’s mind increased, albeit not significantly (t(127) = −.839, p= .403). Within the HLM + booster group, outcome expectations also decreased (Z=−2.037, p= .042), use of a mindfulness exercise to relax also increased (Z=−2.893, p= .004), and motivation to relax Table 6 Description of the booster intervention using the TIDieR checklist (Johnston 2014) Item number and label Booster intervention 1. Brief name A motivational booster intervention to increase students’mindfulness practice 2. Why To increase mindfulness practice at home. The TPB provided suggestions for how to increase practice. 3. What materials ➢Slides on what benefits practicing peers receive ➢Mindfulness: Youth Voices video: https://youtu.be/uOrDmRhwBR8 ➢Cards with benefits associated with mindfulness practice written on them ➢Mindfulness Benefits and Exercises Matching Sheet 4. What procedures One session explaining benefits peers who practice receive and one session encouraging participants to choose benefits and exercises for themselves 5. Who provided Four facilitators who administered the intervention had a background in mindfulness and practiced themselves. Training for the booster intervention: They had attended a two-hour training session delivered by two behavioral scientists and received a manual with scripts to use when addressing the students and assigning the task. 6. How Mode of delivery: face-to-face, group 7. Where Schools in southern Finland 8. When and how much ➢embedded in the HLM mindfulness program’s final 2 sessions ➢1weekintervalbetweenthesessions ➢5 min in the first and 10–20 in the second 9. Tailoring Materials were tailored to be age-appropriate and to fit within the allotted time for delivery, but no individual-level tailoring was included. 10. Modifications Not measured systematically. 11. How well-planned Facilitators were given a checklist and an open-ended comment box to fill in with the materials. Additional, more specific questions were asked 9monthsafter. 12. How well actual Not measured systematically. 320 Mindfulness (2019) 10:312–324