Unlike standardized testing applications of validity, teachers need a simple and efficient way to reflect on the accuracy of the claims based on student performance, then consider whether the uses of those claims are appropriate. A two-phase reasoning process of validation, consisting of a proficiency claim /argument and a use/argument, is presented as a way for teachers to understand and apply the central tenets of validation to their classroom assessments. Since classroom assessment is contextualized with multiple purposes, each teacher is obligated to use validation for their situation. The accuracy of teachers’ conclusions about the proficiency claims, and uses, will depend on their skill in gathering supportive evidence and considering alternative explanations. Examples of the proposed classroom assessment validation process are presented.