The adoption of Next Generation Science Standards (NGSS) and NGSS-like standards necessitates significantly different ways of thinking about K-12 science instruction as well as corresponding instructional approaches to successfully implement the standards. The general stance of the science education community appears to be that, ideally, all teachers will use a research-based constructivist pedagogical approach (i.e., three-dimensional instruction). However, to make this change to constructivist instructional practice and move beyond hypothetical teacher use requires a paradigm shift in how teachers choose to teach. That educators will embrace constructivist epistemology associated with the NGSS is taken as a foregone conclusion. Teachers play an invisible role in the foundational and supporting literature for NGSS and three-dimensional pedagogy, where the hypothetical teacher is addressed only in terms of what practices they need to adopt and what support to provide them. Expectations of teachers’ pedagogical choices in science largely preclude consideration of the complexity and diversity of teachers’ identities. Teachers enact and negotiate their identities in the daily, ongoing classroom-level experiences, not just in their initial development of those identities. To better understand the impact of those identity negotiations on teachers’ instructional choices requires greater breadth and depth of research on identity of science teachers as whole people. In this study I used a qualitative approach with an emphasis on participant narratives. Through interviews, written reflections, and classroom observations, I re-present the stories of how two middle-school science educators’ identities influence their classroom instruction. Both teachers utilize three-dimensional instruction, but their identities manifest primarily in the ways in which they build classroom communities of practice and support the needs of students.