Professional Learning Communities (PLCs) have become increasingly popular in schools. PLCs are groups of teachers, administrators, parents, and students who collaborate to improve their practices and focus on results (DuFour, 2004). Grade-level and department teachers participate in regularly scheduled collaborative team meetings; however, many school leaders lack suitable tools to evaluate fidelity to the PLC model. To address this deficit, we developed a tutorial checklist called the Formative Assessment of Collaborative Teams (FACT) through an action research approach. This article discusses the context of grade-level and department collaborative teams where much of the work of implementing the PLC model takes place. Working alongside practitioners in this context, we developed, implemented, and validated the FACT tool. This article discusses practitioners' reactions to the tool during these processes, including observations conducted using FACT at several schools. The results of this process suggest that FACT is consistent with the elements of effective PLCs, confirming that it discriminates among collaborative teams within and across schools.