The ideas students bring to class and their perspectives on what is happening in the classroom change constantly. Keeping track of these changes is useful for adapting lessons, nurturing student self-reflection, increasing student ownership of learning, and building a teaching practice responsive to learners' needs. In this article, the authors discuss how a simple formative assessment tool--exit tickets--can be used to help teachers do this work. Exit tickets are short response tasks that teachers administer to students after an activity (such as laboratory experiment) or class period. They present opportunities for teachers to elicit students' thinking without affecting their grade, provide individualized feedback, and identify learning needs or modifications to an instructional plan.