Importance: Adults with intellectual and developmental disabilities (IDD) often attend day programs after aging out or graduating from school-based services. Although these programs provide daily structure and social opportunities, occupational therapists remain underutilized despite their expertise in supporting participation and engagement. Objectives: (1) Assess needs, interests, and challenges of adults with IDD. (2) Develop program modules aligned with findings. (3) Evaluate staff perceptions of the modules. Design: Mixed methods applied research design Setting: Day programs for individuals with IDD served as sites for observation and survey recruitment. Participants: Young adults with IDD completed the needs assessment survey (n=21). Great Prospects staff completed the evaluation survey (n=3). Outcomes and Measures: The needs assessment included a survey assessing preferences, perceived needs, and sensory challenges, along with informal observations documenting engagement patterns and sensory-related behaviors. Program evaluation used a modified Systems Usability Scale with open-ended questions to assess perceived usability, satisfaction, relevance, anticipated effectiveness, and OT value. Results: Survey and observational data indicated highest engagement during sensory-rich and movement-based activities. Participants reported sensory regulation challenges and a desire for social and emotional skill-building. Staff rated the OT-designed programming as highly satisfactory, with “good” usability, strong relevance to participants’ needs, and OT value in supporting interaction and engagement. Conclusion and Relevance: Adults with IDD have regulation challenges, social participation barriers, and engagement preferences that complicate program development. OT- designed programming has the potential to promote engagement and support participation by addressing sensory needs, fostering social interaction, and providing structured, meaningful activities.