Background: This study examines the effect of a Theory of Mind (ToM) intervention on ToM abilities and social-emotional functioning in adolescents with developmental language disorder (DLD) or who are deaf/hard of hearing (D/HH). It emphasizes the importance of self-reflection and measurement for personal growth. The research design incorporates both subjective and objective measures to evaluate the intervention's efficacy. Aims: To investigate the impact of the ToM intervention on ToM abilities and social-emotional functioning in adolescents with DLD or who are D/HH. It hypothesizes that participants in the intervention groups will show improved ToM and social-emotional functioning compared with those in the control groups. Methods & Procedures: Adolescents with DLD or who are D/HH were recruited through collaboration with educational institutions. The study utilized a pre-/post-test design, assigning participants to either the intervention or the control group. The ToM intervention involved targeted activities to enhance ToM abilities. ToM abilities and social-emotional functioning were assessed using standardized tests and self-report questionnaires. Statistical analyses compared outcomes between the intervention and no intervention groups. Outcomes & Results: The findings reveal subjective improvements in social-emotional functioning among the D/HH intervention group. However, no significant effects on objective ToM measures were observed. These results highlight the need for further investigation and refinement of interventions in these areas. Future research should focus on improving intervention strategies and exploring additional objective measures to gain a comprehensive understanding of the intervention's impact on ToM and social-emotional functioning in this population. Conclusions & Implications: The ToM intervention shows subjective benefits in improving social-emotional functioning among D/HH adolescents. However, it does not yield significant effects on objective ToM measures. These findings emphasize the ongoing need to refine interventions targeting ToM abilities and social-emotional functioning in this population. Future studies should explore alternative strategies and incorporate additional objective measures to enhance understanding and outcomes.