Responsive teachers need to deal with the unpredictability of classroom interactions. Student thinking can never be fully anticipated despite the most thorough lesson planning. It is very common for teachers to encounter critical moments related to unexpected student ideas or thinking.

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Myhill and Warren (2005) described critical moments as spontaneous unplanned opportunities created by a student utterance. It is ‘a discourse unit in which the teacher’s utterance is significant either in supporting the development of a student’s understanding or in hindering it, or when an opportunity to build on a student’s response was missed’ (p. 59). We developed a series of interactive video cases (Hewitt, Pedretti, Bencze, Vaillancourt, & Yoon, 2003) that capture critical moments encountered by the teachers in Phases 1 and 2 of the project. There are 8 video episodes. They are: