In the past two decades several reform movements in many countries call for higher standards for teachers and teacher education. The central dilemma facing teacher educators is how to educate teachers who can and will conduct quality programs in schools. Reformers argued that quality education may occur when changes take place in teacher education curricula (Feiman-Nemser and Remillard, 1996; Kirk, 1986; Macdonald et al., 2002a; O'Sullivan, 2003; Richardson and Placier, 2001; Wilson and Berne, 1999; Zeichner, 1999). Concurrent with this call for quality teacher education programs has been a call for more research on teachers' professional knowledge. Until now, what we know about teachers' knowledge is rather mystifying. The question of how teachers and under what conditions they construct their knowledge is ...