Twenty years ago when the author was student teaching, he quickly learned what geometry teachers and researchers (e.g., Senk 1985) have long known: High school geometry students struggle with proof. Throughout his career, he has tried to create instructional materials to make proof more accessible to his students. From field-testing materials with…

We analyze the interaction of 3 students working on mathematics problems over several days in a virtual math team. Our analysis traces out how successful collaboration in a later session is contingent upon the work of prior sessions and shows how the development of representational practices is an important aspect of these participants' problem…

In early 2004, Cabrilog released version "II plus" of their interactive geometry package. According to the author, "Cabri Geometry II plus" is clearly a much more useful package than the earlier version. However, unlike other sophisticated applications packages, the designers have avoided creating so many options that secondary students lose their…