Teaching that supports children in scientific sensemaking emphasizes discourse that prioritizes children's ideas and supports children in engaging in disciplinary practices. However, supporting science talk requires skillful instruction, and without support, teachers may find it challenging to engage our youngest students in rich discussions. In this study, we describe the design and implementation of a formative observation tool (the "SOLID Start Tool") that was used as part of online professional learning with instructional coaching. We analyzed interviews, surveys, and videos of professional learning and classroom instruction. We found that teachers and coaches successfully used the "SOLID Start Tool" to (1) provide a vision of high-quality science talk, (2) reflect on current levels of practice, and (3) planning for next steps. We discuss the importance of considering a system of tools to best support K-2 teachers as they shift toward instruction aligned with the Next Generation Science Standards (NGSS).