Background: Children with intellectual disability and specific learning disabilities often lack age-appropriate social skills, which disrupts their social functioning. Because of the limited effectiveness of classroom mainstreaming and social skills training for these children, it is important to explore alternative opportunities for social skill acquisition. Participation in social activities is positively related to children's social adjustment, but little is known about the benefits of activity participation for children with intellectual and specific learning disabilities. Methods: This study investigated the association between frequency and type of social activity participation and the social competence of 8-11-year-old children with intellectual disability (n?=?40) and specific learning disabilities (n?=?53), in comparison with typically developing peers (n?=?24). Results: More time involved in unstructured activities, but not structured activities, was associated with higher levels of social competence for all children. This association was strongest for children with intellectual disability, suggesting that participation in unstructured social activities was most beneficial for these children. Conclusion: Future research on the quality of involvement is necessary to further understand specific aspects of unstructured activities that might facilitate social development.