To promote and support teachers' professional growth in using formative assessment practices in the classroom, we developed and piloted a suite of materials which consists of a set of rubrics for ten dimensions of formative assessment and six self-reflection/peer-observation tools. We describe the iterative development process, the design decisions and challenges, and the findings from an early pilot in which twenty-four educators from five states used the materials. We also report on a content validation study was conducted with seven subject matter experts who confirmed the importance of the ten formative assessment dimensions and did not identify any significant omissions. Finally we have preliminary findings from a group of teachers who engaged with a set of training modules to support their understanding of the rubrics before applying them to classroom practice through peer observation and feedback.