<p>This study aimed to develop and validate assessment tools for assessing rehabilitation outcomes among Thai juvenile offenders. Participants were 422 juveniles from youth training and rehabilitation centers across Thailand. In addition, 441 professionals from eight disciplines, including psychologists, social workers, guidance counselors, nurses, residential caregivers, academic trainers, vocational trainers, and juvenile probation officers responsible for individual case management, assessed the juveniles’ rehabilitation progress. The instruments comprised a juvenile self-assessment questionnaire and eight professional assessment forms completed by professionals involved in the rehabilitation process. These checklist-based instruments were developed using the dynamic risk and protective factors assessment framework as a guiding measurement model. Psychometric properties were examined, including content validity, factorial validity, internal consistency reliability, and known-groups validity. The findings indicated that both professional ratings and juvenile self-assessments demonstrated satisfactory content validity, construct validity, and internal consistency reliability. However, professional-juvenile score discrepancies were substantial, with juveniles generally rating themselves more favorably than professionals. The instruments also demonstrated preliminary postdictive known-groups validity, with moderate classification performance in distinguishing first-time from repeat offenders based on historical recidivism records. Because this evidence was postdictive rather than longitudinal, future follow-up studies are needed to establish prospective predictive validity for recidivism or post-release outcomes.</p>