Numerous initiatives are carried out across the world to support science teaching in early childhood education. However, professional development research shows that in order for teaching interventions to bring about successful changes in practice, it is key that teacher's beliefs, confidence and knowledge change. As a complement to studies showing "how" teachers change, this article examines "why" teachers adopt a pedagogical idea for teaching science in preschool. Drawing on Clarke and Hollingsworth's model for teacher professional growth, the article analyses interviews with teachers that have implemented and developed a pedagogical idea for teaching science in preschool. The results indicate that teachers adopt the pedagogical idea because it helps them to discern and build on science content in everyday practice, which they prefer to their previous way of teaching science through occasional experiments. Further the results show that teachers balance several external influences on what is good preschool pedagogy. The particular pedagogical idea eases that balancing act since it aligns with, and helps teachers to make meaning of, many of these influences.