A discussion is presented on the development and implementation of two inservice training programs for science teachers which were based on a "constructivist perspective" which is based on the belief that knowledge (in an individual) is always a personal construction. Within this framework, the programs involved the development of both teaching strategies aimed at fostering in the pupils the construction of new knowledge in science, and of training activities aimed at fostering in the teachers the construction of a new teaching style. A description is given of the details of the two inservice training programs, the first of which lasted for 5 years and was devoted to inservice science teachers in the middle school level. All were graduated in mathematics or physics, chemistry, biology, or natural sciences. The second, most recent program, was devoted to elementary school teachers who had received very little training in science at the preservice level. (JD)