School psychologists often have reason to suspect that students may not be putting forth full effort during diagnostic tests, or that questionnaire or rating scale data are not credible. However, such suspicions must be tested carefully to yield data-based conclusions. Structured, empirically supported methods for assessing the "response validity" of evaluation data are available, to help gauge effort, motivation, and honesty in clients and informants. The present paper reviews a number of methods, places them in the context of research showing the effects of motivation and incentives on performance, and addresses concerns about including these methods in school-based psychoeducational evaluations. The paper concludes with practical, research-based recommendations for school psychologists when conducting evaluations and writing reports.