Affording children's agency is an important pedagogical underpinning of a high-quality early childhood program. Yet little is known about how teachers' interactions create spaces for children's agency. From the perspectives of ethnomethodology and conversation analysis, this paper investigates how teachers and children navigate agency through their collaborative interactions that relate to classroom participation. Drawing on 170 h of video recordings of classroom interactions in nine preschool classrooms, this paper discusses the teachers' use of 'I wonder...' formulations in their interactions with children. In total, there were 17 occasions where the teachers used this formulation to create a space for agency for children to make decisions regarding their participation in classroom experiences. The 'I wonder...' formulation is suggested as a strategy for teachers to use when inviting classroom participation at times when children really do have a choice. These findings contribute to understanding children's agency and point to practical strategies for teachers to afford children agency within the bounds of classroom life. Building and using a repertoire of pedagogic strategies to encourage child participation and agency is demonstrable evidence of high-quality teacher-child interactions. (author abstract)