Effective mathematics teaching elicits and uses evidence of student thinking to assess progress toward mathematical understanding and adjusts instruction continually to support and extend learning (National Council of Teachers of Mathematics, 2014). However, as teachers march through content in precalculus, they tend to rely heavily on traditional tests and quizzes that focus on procedural skills and correct or incorrect answers without giving them an opportunity to identify and address misconceptions. This article examines an alternative to a traditional test on functions that is a project where students create a children's story based on a rate function. This approach gives teachers better insight into students' thinking while continuing to deepen their mathematical understanding. Milestones are incorporated throughout the project to gather evidence of student understanding and enable adjustments to instruction.