Although high-stakes testing is now widespread, methods for evaluating the validity of gains obtained under high-stakes conditions are poorly developed. This report presents an approach for evaluating the validity of inferences based on score gains on high-stakes tests. It describes the inadequacy of traditional validation approaches for validating gains under high-stakes conditions and outlines an alternative validation framework for conceptualizing meaningful and inflated score gains. The report draws on this framework to suggest a classification of forms of test preparation and their likely effects on the validity of gains. Finally, it suggests concrete directions for validation efforts that would be consistent with the framework. An appendix contains a mathematical model of the validity of gains. (Contains 3 figures and 23 references.) (Author/SLD)