This study reports on the professional learning of two teachers of science who were learning to engage their grade four students in meaningful, hands-on learning. Teachers' learning took place in the context of a 10-month university-based action research program designed to help improve the practice of science, technology, engineering and mathematics (STEM) Kindergarten to grade 9 teachers. Post-project analysis relied on Cultural Historical Activity Theory and its principle of expansive learning. Findings revealed that expansion of teachers' community served as a catalyst in their adoption of new tools. These included action research tools, pedagogical tools and information and technology tools. To capitalise on the affordances of the tools, the norms and division of labour needed to expand. Norms of practice shifted to an iterative process of design, implementation and observation and redesign of students' learning. Teachers expanded the division of labour from a position of vertical, teacher-centred direction and instruction to one in which they became facilitators of learning.