The theory and research presented address teachers’ pedagogical content knowledge about children's minds and learning as they relate to teacher education. The theory suggests that without determining the nature of teachers’ mental models about children's minds and learning before instructors teach them preservice and inservice courses, instructors will r.ot be able to engage the mental models they have about those areas. And if instructors do not engage those mental models, they are likely to remain unchanged, Two studies were conducted to uncover teachers’ implicit, unreflective mental models about children's minds and leaning when teachers spoke about instruction (espoused mental models) and when they actually taught (in-use mental models). In the former, teachers have a mental model resembling information-processing models from the cognitive sciences. In the latter, teachers have a mental model whose main unit is meta-assumptions about children's minds. These meta-assumptions constrain the cognitive goals they want to achieve in their pupils and the teaching methods they employ to achieve those goals. In a third study, my research team and I tested the effects of an inservice teacher training course that attempted to make explicit teachers’ implicit espoused and in-use mental models and to connect them.