Although a number of studies have associated recasts with second language development, the actual mechanisms by which recasts work to impact learning are still little understood. In particular, researchers have sought to gain a deeper understanding of the connections among recasts, learners' responses to recasts, and subsequent development. To this end, the current study examines the impact of recasts and different types of responses on English as a second language (ESL) question development. In a pretest-posttest design, 58 Thai English as a foreign language university students carried out a series of communicative tasks with native English speakers and completed four tests over a 9-week period. The learners' treatment task data were analyzed for the occurrence of recasts and responses to recasts that targeted developmentally advanced question forms. Their test data were examined for evidence of advancement to a higher stage in the developmental sequence for question formation. Results indicate that recasts were a significant predictor of ESL question development. Learners' responses in the form of primed production of the question forms targeted in the recasts were also predictive of ESL question development, but responses in the form of immediate repetitions of recasts were not associated with development.