Background: Adults with intellectual disability are often disengaged in disability services. While Active Support has found efficacy in residential settings, less is known in day services. This study examines the impact of Active Support in day services for adults with intellectual disability in Singapore, particularly on engagement and behaviours of concern. Method: An experimental design was used, with a group of 32 participants receiving an Active Support programme over 6 months, compared to a control group of 16 participants with treatment as usual. Time sampling of behaviours was conducted every 4 weeks. Results: The Active Support group saw increases in activity engagement and social engagement with staff, and decreases in disengagement and stereotypical behaviours, compared to the control group over time. Conclusion: Results support the implementation of Active Support across other day services for adults with intellectual disability. Active Support principles should be considered in planning policies and service outcome measures.