An adapted alternating treatments design was used to compare the expressive use of thematic vocabulary by three preschool children with developmental delays during Dialogic Reading, a shared book reading intervention, and Activity-Based Intervention, a naturalistic play-based teaching method. The design was replicated across two early childhood themes. For each theme, five vocabulary words were randomly assigned to Dialogic Reading, Activity-Based Intervention, or a control condition. Intervention was delivered 2 times per day for 5 days across 2 weeks. Results suggest both methods increased children's use of target vocabulary and were similarly effective for increasing expressive use of thematic vocabulary by preschoolers with disabilities. (author abstract)