To support elementary students' learning of core, standards-based life science concepts highlighted in the "Next Generation Science Standards," prospective elementary teachers should develop an understanding of life science concepts and learn to apply their content knowledge in instructional practice to craft elementary science learning environments grounded in students' thinking. To do so, teachers must learn to use high-leverage instructional practices, such as formative assessment, to engage students in scientific practices and connect instruction to students' ideas. However, teachers may not understand formative assessment or possess sufficient science content knowledge to effectively engage in related instructional practices. To address these needs, we developed and conducted research within an innovative course for preservice elementary teachers built upon two pillars--life science concepts and formative assessment. An embedded mixed methods study was used to evaluate the effect of the intervention on preservice teachers' (n = 49) content knowledge and ability to engage in formative assessment practices for science. Findings showed that increased life content knowledge over the semester helped preservice teachers engage more productively in anticipating and evaluating students' ideas, but not in identifying effective instructional strategies to respond to those ideas.