This study examined the influence of teachers' instructional moves on students' relational thinking during small-group collaborative discussions. One hundred and twenty 4th grade students and 6 teachers participated in a series of 10 discussions, generating a video-recorded corpus containing 32,511 turns for speaking. A microanalysis of a subset of the corpus showed that teacher prompts for relational thinking, rather than lower level prompts or prompts for evaluation, had an immediate effect on student relational thinking, triggering further relational thinking from students over several speaking turns. Students were unlikely to emulate a teacher's relational thinking strategy but highly likely to emulate another student's. Behavioral management but not cognitive management increased the likelihood of relational thinking. Specific praise for cognitive or social strategies enhanced relational thinking, and the bidirectional association between praise and relational thinking suggested a transactional model of teacher--student interaction. The results underscore the importance of teacher influences in peer collaboration, even when the absolute rate of teacher talk is low.