Research documents the negative impact of physical and social environmental barriers on engagement in school, work, and the community for youth with intellectual and /or developmental disabilities (IDD). Project "TEAM" (Teens making Environment and Activity Modifications) was designed to teach youth to systematically identify environmental barriers, generate modification strategies, and request accommodations. This formative evaluation used a mixed methods expansion design to investigate outcomes, activities, and experiences. Trainees had a significant increase in knowledge of environmental factors and modification strategies but no changes in applied problem-solving. 76% attained at least one goal as measured through goal attainment scaling. Intervention activities ranged in quality. Trainees enjoyed the interactive and applied aspects of Project "TEAM" but found some concepts and materials difficult to understand. Lessons learned from this comprehensive evaluation can inform future revisions to Project "TEAM" and may be equally relevant for other researchers evaluating programs targeting transition-age youth with IDD.