Mediational activities in a dynamic geometry environment and teachers' specialized content knowledge

Dynamic geometry environments can support learning of geometry through mediating learners' activity. To understand how dynamic geometry environments mediate the activity of mathematics teachers, we used Rabardel's categories of tool mediations in an instrument-mediated activity. We analyzed the discursive and inscriptive interactions of 4 mathematics teachers who worked for 15 weeks as a team to construct geometric figures and solve open-ended geometric problems in a collaborative, dynamic geometry environment. Teachers' specialized content knowledge was evident when they used the environment epistemically. In addition to Rabardel's epistemic and pragmatic mediations, we found and coined a third mediation-pedagogic mediation-by which teachers use the environment to help other team members understand particular geometric objects and relations among them. Understanding how teachers use technological tools can inform the design of professional development programs that engage them with such tools to extend their specialized content knowledge.