Youth’s structured (e.g., sports) and unstructured (e.g., socializing) activities are key contexts for positive development. Both behavioral participation (e.g., frequency) and elements of psychological engagement (e.g., enjoyment, challenge) in programs and activities have been linked to components of youth development. We tested a model in which both psychological engagement and behavioral participation in activities predicted overall positive youth development in older adolescent and emerging adult samples (Sample 1, n = 235, mean age = 18.7 years, SD = 1.4 years, 67.7% female; Sample 2, n = 186, mean age = 20.0 years, SD = 2.1 years, 68.8% female). In the first known study to include behavioral participation and multidimensional psychological engagement in predicting the Five Cs of positive youth development, we found that greater psychological engagement, but not behavioral participation, was related to higher positive youth development across samples and different activity types. Findings suggest that promoting youth’s psychological engagement in programs and other activities, rather than just their physical presence, may be advantageous for strengthening positive youth development.