The study reported in this paper, a Multistage Longitudinal Comparative (MLC) Design Stage II evaluation conducted as a planned preliminary efficacy evaluation (psychometric evaluation of measures, short-term controlled outcome studies, etc.) of the Changing Lives Program (CLP), provided evidence for the reliability and validity of qualitative measures under development as well as the utility of unifying qualitative (e.g., open coding, theoretical sampling/saturation, etc.) and quantitative (e.g., quasi-experimental designs, advanced statistical analysis, psychometric analysis, etc.) research methods and procedures for evaluating intervention programs. Specifically, when analyzed using Relational Data Analysis, response data from the Future Possible Selves Questionnaire yielded theoretically meaningful categories with robust levels of reliability and construct and concurrent (external) validity. Additionally, the pattern of qualitative change for participants in the intervention condition, the CLP, were found to be positive, significant, and in the hypothesized direction relative to the comparison group, providing support for the feasibility of creating evidence-based youth development programs for promoting positive development in self and identity in troubled youth. (Contains 1 table and 1 figure.)