The aim of this study was to identify when and how the interactive whiteboard (IWB) functioned as a productive tool that impacted student learning in mathematics. Using video data, field notes, and interview transcripts from 1 school year in two optimal case study classrooms, we were able to examine the unique opportunities afforded by the size of the IWB screen, the manipulation of virtual objects onscreen, and related communication using gestures. We: (i) established criteria for defining "significant learning moments"; (ii) assessed these significant learning moments to determine how the interactive whiteboard was supporting the learning; and (iii) isolated the use of gesture during IWB use to magnify the grain size of our analysis and understanding. The data fell into three types of IWB use: productive (89%), reproductive (2%), and problematic (9%). The study recommends that in order to best support student learning, professional development for teachers should emphasize direct and active "student" use of the IWB to engage students in inquiry of mathematics. (Contains 4 tables.)