Background: When delivered in a safe space, programs effective in promoting positive youth development (PYD) involve key features termed the Big Three: (1) Positive and sustained adult-youth relationships; (2) Life-skill-building activities; and (3) Opportunities for youth contribution and leadership. However, no measures exist in the literature for assessing the Big Three. Objective: The present study sought to develop a quantitative measure of program quality. Method: Using data collected from Rwandese participants from the Compassion International (CI) Study of PYD, we developed a youth-report measure with two groups: 603 youth enrolled in CI-supported programs, and 320 youth not enrolled in CI but involved in other youth development programs (total N = 923, M[subscript age] = 11.81 years, SD = 1.68). We used exploratory and confirmatory factor analyses to refine the item pool. Using a propensity-score matched subsample, we added a measure of youth contribution to assess predictive validity of the measure, and tested for between-group measurement invariance across age, gender, and CI-enrollment status. We then compared CI-supported and non-CI-supported youth as an initial assessment using the measure. Results: We established a parsimonious and robust measure of the Big Three demonstrating strong psychometric properties. CI-supported-youth reported higher levels of each of the Big Three features. Conclusions: These results provide information about the usefulness of a measure assessing the Big Three attributes of effective PYD programs. We discuss how future research using this approach to understanding the content of youth development programs may provide evidence of how PYD may be promoted.