"Many educators think of formative assessment as another kind of test. Instead, it is a process to help instructors understand their students' day-to-day learning and develop appropriate interventions to improve that learning," says Nancy Gerzon, Senior Research Associate at WestEd. "We know from research that effective formative assessment has multiple components, but most educators use only one or two." Gerzon directs the New York Formative Assessment Project, which aims to change how educators think about formative assessment. The initiative is led by a New York Comprehensive Center (NYCC) Assessment Team, with support from the Assessment and Accountability Comprehensive Center at WestEd. The New York State Education Department and the Syracuse City School District also are partners. According to Gerzon, research shows that students make dramatic achievement gains when teachers break instructional units into a progression of clear, well-defined learning targets; involve students in setting learning goals and assessing their progress; give immediate and corrective feedback; and set up peer collaboration activities to build content mastery. Known as formative assessment, this comprehensive and interactive process is a model of mastery learning, in which a student progressively develops skills and confidence under the guidance of a professional. This article describes how this initiative was implemented.