According to the National Research Council (NRC 2007), three critical components significantly influence students' science learning: teacher knowledge, teachers' opportunities to learn, and instructional systems. If students' science achievement is strongly correlated with teachers' science competence, and core competencies are central to professional development, then access to quality professional development needs to be a priority. The purpose of this article is to first outline how professional development experiences can best be structured to support teachers' science learning, leading to quality science instruction and learning for students. This discussion highlights four key principles central to effective professional development: (1) Seeing professional development as a social enterprise; (2) Maximizing the social enterprise within democratic learning communities; (3) Seeing adults as active science learners; and (4) Development proceeding from science learners to science mentors. The author will demonstrate how to satisfy these same key principles when using an instructive framework for physical science professional development in early childhood education (preK-grade 2). (Contains 3 online resources.)