Students may not fully demonstrate their knowledge and skills on accountability tests if there are no stakes attached to individual performance. In that case, assessment results may not accurately reflect student achievement, so the validity of score interpretations and uses suffers. For this study, matched samples of students taking state accountability tests under low-stakes and high-stakes conditions were used to estimate the effect of stakes on test performance and subsequent pass rates. Across five assessments, expected performance was greater under high-stakes conditions, with effect sizes ranging from 0.41 to 0.50 standard deviations and with students of lower ability tending to be slightly more affected by stakes. Depending on where cut scores were set, pass rates differed by up to 30% when comparing the low- and high-stakes conditions.