Educational systems in the United States are generating vast amounts of data on student achievement. This may provide researchers and policy makers with long sought-after insight on the factors explaining student performance. This study uses recent data from Washington 10th graders to examine why some students learned more math than others. Although important differences appear to exist among schools and districts, the data are of limited use in explaining student performance. The article discusses some of the possible reasons for this and the implications for education policy. (Contains 7 tables and 12 notes.)