This study examined the transactional, utterance-by-utterance dependencies in the syntactic complexity of teachers' and children's talk during small-group conversations in preschool classrooms. The sample included 39 teachers and select children in their classroom, which targeted enrollment to children experiencing documentable risk factors. Patterns of sequential dependencies demonstrated a bi-directional interdependence in teachers' and children's complex syntactic use, whereby both teachers and children appeared sensitive to each other's use of complex syntactic forms. Teachers' use of complex syntax increased the likelihood that children's adjacent utterance would contain complex syntax; similarly, children's use of complex or simple syntax increased the likelihood that teachers' adjacent utterance would mirror their syntactic level. Associations were small to moderately large in strength, but varied across individual classrooms. The findings point to complex, bi-directional relationships underlying the complexity of talk within the classroom language environment. (author abstract)