Background/Context: Despite problems with accountability systems under No Child Left Behind, the policy has been widely commended for exposing the depth and breadth of educational inequality in the United States. As states implement new accountability systems, there is growing concern that attention to achievement gaps and the performance of marginalized children has faded. Many approved accountability plans no longer report achievement by student subgroups or include subgroup performance in the calculation of accountability indicators. Research Purpose: This study examined the informational significance of Oklahoma's A-F accountability grades relative to the policy objective of achievement equity. Informational significance as explained in self-determination theory provided a framework to explore the usefulness of an A-F grade for understanding achievement differences within and between schools. Research Design: We evaluated the informational significance of Oklahoma A-F school grades by analyzing reading and math test scores from over 25,000 students in 81 elementary and middle schools. The study was designed to address two questions: Do students in "A" and "B" schools have high average achievement and small achievement gaps compared to students in "D" and "F" schools? What is the difference in average achievement and achievement gaps between school grades when holding constant contextual school conditions? Results: We found test score gaps attributed to Free and Reduced Lunch qualification and minority status. Free and Reduced Lunch and minority students average about one standard deviation lower in math and reading than their peers. Test score gaps varied across A-F school grades with the largest gaps existing in "A" and "B" schools. HLM results showed that A-F grades do not differentiate schools by effectiveness levels. For reading, we did not find statistically significant main effects attributed to letter grades. For math, the only statistically significance difference was between students in "A" and "B" schools and students in "F" schools. This difference had a small effect size. School grades did moderate achievement gaps, but gaps moved in a direction opposite from what would be desired of an accountability system that measured achievement equity. Conclusions: Progress made under NCLB in exposing achievement inequity in the U.S. has taken a step back with Oklahoma's A-F school grades. Our evidence suggests that a composite letter grade provides very little meaningful information about achievement differences.