Instructional shifts required by equitable, reform-based science instruction are challenging, especially in the elementary context. Such shifts require professional development (PD) that supports teacher internalization of new pedagogical strategies as well as changes in beliefs about how students learn. Because of this complexity, many PD programs struggle to foster lasting pedagogical shifts, necessitating further investigation into why some teachers successfully embrace reform practices while others do not. This qualitative study uses a nonlinear, iterative model of teacher learning (Interconnected Model of Professional Growth; Clarke & Hollingsworth, 2002) alongside professional noticing to help understand why elementary teachers in science PD differentially make sense of and internalize new pedagogies. Findings indicate that teachers most likely to adopt reform-based instructional practices from the PD were those who clearly connected student learning to their instructional moves. In addition, teachers who more actively attended to student sensemaking and productive struggle took up pedagogies from the PD more substantively than did colleagues who attended solely to student engagement and affect. Finally, teachers who attended to and valued novel ideas from students' lived experiences were more likely to change their beliefs about students' capacity to learn science, and thus more likely to see the value of instructional practices from the PD. In sum, structuring PD to build on these specific teacher noticing skills can encourage more teachers to move away from traditional, teacher-directed instructional practice, and more fully support reform-based instructional practices.