ORIGINAL PAPER Effectiveness of the Mindfulness-Based OpenMind-Korea (OM-K) Preschool Program Eunjin Kim 1 & Monica M. Jackman 2 & Seong-Hun Jo 1 & Jisun Oh 1 & Shi-Yong Ko 1 & Carrie L. McPherson 3 & Yoon-Suk Hwang 4 & Nirbhay N. Singh 5 # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Objectives Preschool years provide a window of opportunity to enhance attentional flexibility, increase inhibitory control, build resilience, and strengthen emotion regulation in children. We assessed the effectiveness of a mindfulness-based social-emotional learning program—OpenMind-Korea (OM-K)—on preschool children’ s emotion regulation, resilience, and prosocial behaviors. Method In a two-arm randomized controlled trial, two of four preschools were randomly assigned to the intervention condition and two to the control condition. The teachers in the intervention condition implemented the OM-K program (n = 42 children), and the teachers in the control condition provided instruction as usual (n = 41 children). Results At baseline (pre-intervention), the children in the control condition were rated as being significantly better on all outcome variables than those in the intervention condition. Although children in the intervention condition improved on all outcome variables, the children in the control condition continued to be rated higher on all outcome variables at the first post-intervention assessment. However, the children in the intervention condition were rated with significantly higher scores than the children in the control condition at the second and third post-intervention assessments. The children in the intervention condition were rated with significantly higher scores on lability/negativity, resilience, and prosocial behaviors. Although the ratings for adaptive regulation were higher for the children in the intervention condition than those in the control condition, the ratings did not reach statistical significance. Conclusions This study suggests that implementing the OM-K program in preschools may enhance the children’ s emotion regulation (adaptive regulation, lability/negativity), resilience, and prosocial behavior (helping, sharing, cooperation, and comfort to others). Keywords OpenMind-Korea . Social-emotional learning . Preschool . Mindfulness . Emotion regulation In terms of neural plasticity, early childhood is an important developmental period during which children learn self- regulation skills (Fjell et al. 2012; Posner and Rothbart 2009). Self-regulation refers to the child’ s volitional control of attention, thoughts, emotions, and action. Increasing de- mands are placed on preschool children’ s self-regulation and social skills as they transition to kindergarten (Rimm- Kaufman et al. 2000). Preschool children who have inade- quate self-regulation skills are at risk for low academic en- gagement, poor academic outcomes, and peer rejection (Blair 2002; Ladd et al. 2006), and behavioral difficulties (Raver et al. 2009). Given that preschool years are a period when specific brain regions are particularly modifiable, it of- fers a window of opportunity to provide enrichment and train- ing that enhance attentional flexibility, inhibitory control, and effective emotional regulation when faced with adverse events or situations (Dickinson et al. 2006; Ursache et al. 2012). A number of preschool programs have been developed that focus on specific aspects of self-regulation. For example, the Research-Based Developmentally Informed (REDI) Head Start program (Bierman et al. 2008a, b) includes language * Eunjin Kim ejkim2367@wku.ac.kr 1 Institute of Mind Humanities, Wonkwang University, Iksan, Republic of Korea 2 Little Lotus Therapy and Consulting, Port St. Lucie, FL, USA 3 McPherson Therapy and Consulting, Greenville, KY, USA 4 Institute for Learning Sciences & Teacher Education, Australian Catholic University, Brisbane, Queensland, Australia 5 Department of Psychiatry and Health Behavior, Medical College of Georgia, Augusta University, Augusta, GA, USA Mindfulness https://doi.org/10.1007/s12671-020-01337-2