The present article describes research carried out with four student teachers of primary and secondary science education. The preservice teachers' conceptions of the learning and teaching of science were analyzed and compared with their classroom practice when teaching science lessons. The data gathering procedures included a questionnaire and interviews, both analyzed by means of cognitive maps, and classroom observations during the participants' practice teaching. The results did not allow a general correspondence to be established between preservice teachers' conceptions about teaching and learning science and their classroom behavior. The implications of the research for teacher education are discussed