The Assessing for Change in Chemical Thinking (ACCT) is a NSF-funded collaboration focusing on fostering chemical thinking in secondary and tertiary learning environments through strategic formative assessment usage. It grew out of the Chemical Thinking Learning Progression project, which is studying how students develop understanding of chemistry from middle school through undergraduate completion. Learning progressions are cognitive models that describe pathways of how the learning of ideas and abilities develop over time. The Chemical Thinking Learning Progression focuses on three main types of practices in chemistry: sense-making through investigating the properties and behaviors of chemical systems, problem-solving through designing substances or processes to address modern problems, and evaluating the social, economic and environmental costs and benefits of chemical products and activities. The overall project has three emphases: (a) study students’ learning progress along domain-general and chemistry-specific progress variables that include conceptual sophistication and modes of reasoning, (b) develop resources, tools, and professional development for teachers of chemistry to foster students’ chemical thinking, and (c) study how chemistry teachers’ assessment reasoning changes and what chemistry teachers’ emphasize as formative assessment is used as a lever for change.