Nonverbal coordination and affect regulation in play: Pathways to therapeutic change in Mentalization-Based Treatment...

Nonverbal interventions are central to child psychotherapy and play a key role in enhancing in-session affect regulatory processes that may ultimately contribute to treatment outcomes; however, empirical evidence examining their role in therapeutic change remains limited. The present study investigated whether therapists' nonverbal coordination predicted treatment outcomes in Mentalization-Based Treatment for Children through improving children's in-session affect regulation in play. The sample comprised 95 children (M_age = 7.80 years, 37.9% girls) with internalizing and externalizing problems and their 16 therapists, who provided Mentalization-Based Treatment for Children within the context of a clinical trial. Two hundred forty-five therapy sessions from early, middle, and late phases of treatment were coded for therapists' nonverbal coordination and children's in-session affect regulation characteristics in play. Child outcomes included parent-reported emotion regulation and total problem levels assessed at baseline, midtreatment, and posttreatment. Multilevel mediation analyses indicated higher levels of therapists' nonverbal coordination significantly predicted better in-session affect regulation in play. In turn, in-session affect regulation in play predicted lower total problem levels and higher overall emotion regulation over the course of treatment. Indirect effects of nonverbal coordination on both outcomes via in-session affect regulation in play were significant, whereas direct effects were not, indicating that nonverbal coordination was associated with outcomes primarily through in-session affect regulation. Findings suggested that therapists' nonverbal coordination supports therapeutic change in Mentalization-Based Treatment for Children by enhancing children's affect regulatory capacities within play, which may facilitate broader improvements in emotional and behavioral functioning. (PsycInfo Database Record (c) 2026 APA, all rights reserved).