In order to achieve the vision of the Framework for K12 Science Education and the Next Generation Science Standards (NGSS), science instruction must be supported every day, all year and in all grades. Our project seeks to understand what kinds of supports are needed to help science teachers act as leaders in their buildings in order to promote sustainable science instruction aligned with NGSS, in the context of a large urban district. The Supporting Middle Grades Science Professional Development in CPS: Content, Curriculum, Coaching and Using Data Project (CCCUD Project) aims to strengthen systems of continuous improvement for building whole-school capacity to implement science instruction aligned with the NGSS. The systems include support for K-8 science teachers’ in-school and cross-school collaboration through coaching and professional learning community (PLC) sessions where tools and strategies for teacher-teacher and teacher-administrator collaboration are shared. PLCs focus on teacher leadership and formative assessment in science. In PLCs, teachers formatively assess student work utilizing the Claims Evidence and Reasoning framework and attempt to reach consensus on individual students’ understanding of the content as well as a common understanding of what NGSS-aligned student work looks like. Participants show growth in student engagement in the NGSS Science and Engineering Practices, teacher leadership characteristics and behaviors, and use of formative assessment strategies over time in the project.