The relationship between teachers and Computer Algebra Systems is generally problematic. The extensive capabilities of CAS provide opportunities for learning but also bring a new complexity that makes it difficult for teachers to take advantage of these opportunities. Barzel's paper contrasts with this observation: in a "Lernwerkstatt" (translated: learning workshop) project teachers were brought to accept changes in their classroom activities and management that accompanied the introduction of CAS. The project actually took into consideration the teachers' need to control the "didactical time" and their "praxeological" needs. It seems that it contributed much to making CAS acceptable to teachers. Another feature contributing to this success is the decision to limit the Lernwerkstatt project's mathematical area to polynomials. In other areas of mathematics, standard CAS are very problematic with regard to secondary education curricula, creating difficulties for the teacher. That is why this reaction also introduces a discussion about the design of CAS tools for classroom use. (Contains 3 figures.)