The document discusses the importance of formative data and data-driven decision making (DDDM) in schools. DDDM involves using frequent and ongoing assessments to gather insights into student learning, which teachers can then use to improve instruction. This is different than external accountability measures like No Child Left Behind. The document outlines nine essential elements of effective data-driven professional learning communities, including formative assessments, regular team meetings, and using data to inform instructional changes. When implemented well through a collaborative process, DDDM can significantly improve student achievement according to research.