This article details the development of the Youth Development Assessment Device (YDAD), an instrument designed to measure a youth's experiences within youth development programs. A total of 1,074 adolescents, between 12 and 18 years of age, participated in the study. Exploratory factor analysis yielded three factors: Supportive Environment, Emotional Safety and Wellbeing, and Involvement and Challenge. Moderately high Cronbach's alphas indicated that scores from the YDAD subscales were internally consistent. Confirmatory factor analysis was used to examine the fit of the model and to test convergent and discriminant validity of YDAD scores. The use of the instrument in process evaluations is described. Implications for future research are discussed.