This brief is the first in a series that highlights key features of high-quality instruction for English learners, and the role formative assessment plays in their success. Formative assessment supports teachers to enact these features by providing them with tools to gauge and react to student learning in real-time. These practices also support students to assess their own learning which enhances their sense of agency. Overall, the series illustrates how instructional methods and assessment practices work together to improve English learner outcomes.