The purpose of the present study is to investigate the mediational function of the gesture-speech interface in the instructional conversation that emerged as teachers attempted to explain the meaning of English words to their students in two EFL classrooms in the Ukraine. Its analytical framework is provided by Vygotsky's sociocultural psychology (e.g., Lantolf & Thorne, 2006) and McNeill's (1992, 2005) theory of gesture-speech synchronization, in particular his notion of "catchment"--recurrent gestural features that perform a cohesive function. Although the interactions between teachers and students were brief, lasting a mere one minute and fourteen seconds, they were pedagogically rich and remarkably informative regarding the role of gesture in classroom instructional conversations. The analyses suggest that the gesture-speech interface is a potent mediational tool through which students imagistically display details of their understandings of L2 word meanings that do not always emerge through the verbal medium alone. For their part, the teachers integrated gesture into their instructional talk as a way of remediating and improving student understandings. Finally, students signaled their modified understandings by appropriating and using the teachers' gestures in their own expressive moves. (Contains 5 notes and 6 figures.)