In educational practice, test results are used for several purposes. However, validity research is especially focused on the validity of summative assessment. This article aimed to provide a general framework for validating formative assessment. The authors applied the argument-based approach to validation to the context of formative assessment. This resulted in a proposed interpretation and use argument consisting of a score interpretation and a score use. The former involves inferences linking specific task performance to an interpretation of a student's general performance. The latter involves inferences regarding decisions about actions and educational consequences. The validity argument should focus on critical claims regarding score interpretation and score use, since both are critical to the effectiveness of formative assessment. The proposed framework is illustrated by an operational example including a presentation of evidence that can be collected on the basis of the framework.