Outcome Patterns of SPT-SAFE and DBT-BI in Adolescents with Suicidal Ideation and Non-Suicidal Self-Injury: A Retrospective School-Based Study

Background/Objectives: Adolescent suicidal ideation and non-suicidal self-injury (NSSI) are major public health concerns, yet differences between active interventions are often modest. This retrospective study provides preliminary descriptive evidence regarding short-term symptom change across two school-based intervention pathways—Sandplay Therapy with Suicidal ideation and Self-injury Focused Engagement (SPT-SAFE) and a Dialectical Behavior Therapy-informed Brief Intervention (DBT-BI)—in a clinical sample of middle- and high-school adolescents with suicidal ideation and NSSI. Methods: Archival clinical records from 112 adolescents treated in a school-based suicide prevention center were analyzed retrospectively. The sample included 52 adolescents who received SPT-SAFE and 60 who received DBT-BI. Outcomes included suicidal ideation, NSSI frequency, depressive symptoms, anxiety, aggression, impulsiveness, and self-concept. Pre–post changes were examined using mixed-design ANOVAs, with baseline-adjusted ANCOVAs conducted as supplementary analyses. Given the retrospective and clinically assigned design, findings were interpreted as observational associations rather than causal treatment effects. Results: Both intervention groups showed significant pre–post improvements across multiple outcome domains. Overall between-group differences were limited. A nominal, uncorrected Group × Time interaction was observed for impulsiveness, with the DBT-BI group showing a descriptively larger pre–post decrease than the SPT-SAFE group. However, this effect was small and did not remain statistically significant after Bonferroni correction or Benjamini–Hochberg false discovery rate correction across the seven interaction tests. No other outcome showed a multiplicity-adjusted Group × Time interaction. Conclusions: The present study did not provide robust multiplicity-adjusted evidence for differential treatment effects between SPT-SAFE and DBT-BI. The nominal impulsivity finding should be interpreted only as a small, uncorrected exploratory signal for future hypothesis generation. The contribution of this study is therefore descriptive and preliminary, characterizing short-term symptom change in a treatment-engaged adolescent completer sample within a routine school-based service system, rather than supporting domain-specific comparative efficacy or domain-sensitive intervention planning.