An important task for the preschool teacher is to create meaningful learning situations where children have opportunities to experience science. However, many teachers have both weak subject knowledge and a lack of confidence to teach science. The aim of the project presented in this article was to capture how nine preschool teachers developed their learning of and self-confidence in teaching science during a two-year professional development (PD) project while coplanning, coteaching, and coreflecting on their teaching activities. During the project, the preschool teachers' self-confidence and attitudes played an important role for the their approach to science activities. Their collaborative learning and reflection became important for their PD and for the way science phenomena were included in the preschool context. As such, the project is based on opportunities for preschool teachers to develop their ideas about science and to reframe their work with the aim to stimulate children's curiosity for science. (author abstract)