For every teacher, the curriculum is clearly important: it can be in agreement with the way he thinks about mathematics or it may differ profoundly from his view. The position held will influence the sense that the teacher gives to his teaching, and different positions will not produce the same type of knowledge. Changes to the curriculum therefore provide a stimulus to reconsideration which, depending on one’s attitude, may produce an unrestrained « proselytism » or an attitude of complete rejection. This conflict between teachers can often also be found, to a lesser degree, present in each teacher. The purpose of this article is to propose frameworks for thinking about change which provide for an objective approach to the analysis of the effects produced. The specific example to be studied concerns the changes to the mathematics curriculum for the college (11 – 15 yrs) which took place in France from 1986 to 1989, and deals with the treatment of « Thales ». (ZDM/Mathdi)