ABSTRACT
This chapter covers research on the work of teaching in geometry and research on teachers' knowledge of geometry. It starts with some framing considerations for the study of geometry teaching, discusses instructional situations in the teaching of geometry, and eventually moves to discussing teacher knowledge of and beliefs in geometry. Ordinary geometry instruction relies on a number of instructional situations to facilitate students' learning of geometric concepts. Instructional situation is a quite general concept, used to describe the mathematical work done in classrooms both in terms of specific tasks that students do and in terms of curricular items targeted with such type of tasks. The use of Dynamic Geometry Software (DGS) was first studied from the point of view of its impact on the practice of established teachers who got acquainted with the new technology and made its use part of their teaching praxeologies.
