GEOMETRIC FIGURES FROM MIDDLE TO SECONDARY SCHOOL: MEDIATING THEORY AND PRACTICE

Abstract. This paper concerns a recent work carried out with a group of 6 expert teachers who changed their school level at the beginning of this year. The work is a continuation and an adaptation of an experience that has been going on for some years with several teachers from high schools. The theoretical aspects involve questions on the teaching of elementary geometry, van Hiele's theory of levels and teachers ' conceptions on the role of definitions and their teaching. We conducted four discussion sessions on these arguments following a designed precise plot in order to encourage teachers to reflect on their own practice, on their curricular activity and on their teaching aims. Prologue, or the first “match ” between theory and practice Between 1998 and 2001 the authors used Van Hiele's theory as a means to facilitate secondary school teachers in discussing students ' performances on agreed worksheets on geometry (Cannizzaro & Menghini, 2001). The main purpose was to enhance their didactical awareness in managing pupils ' transition from the perception of an elementary figure to its definition and from definitions t