In addition to reporting overall data on student performance, states and districts also disaggregate the data to show the performance of particular groups of students. The Title I statute requires states and districts to report the performance of students by race, gender, economic status, and other factors. This requirement was intended to ensure that states and districts do not neglect disadvantaged students.
Disaggregating data helps provide a more accurate picture of performance and makes it possible to use assessment data to improve performance. For example, one state examined two districts that had vastly different overall rates of performance. But when state officials broke out the data by race and poverty, they found that poor black students performed roughly equally in both districts. This finding suggested that the higher-performing district's overall scores reflected its success with the majority of students, not all students.
This kind of information can be quite powerful. Rather than rest on their laurels, the high-performing district can look for ways to adjust its instructional program for poor black students. That suggests a strategy that might not be apparent if the district looked only at overall results.
In addition, states and districts can use disaggregated results to see the effects of their policies and practices on various groups. It may be, for example, that implementing a new form of assessment without changing the conditions of instruction in all schools could widen the gap in performance between white and black students. By looking at results for different groups of students, districts and states can monitor the unintended effects of their policies and make needed changes.
The idea of disaggregation stems in part from a substantial body of literature aimed at determining the effects of schooling on student performance (Raudenbush and Willms, 1995). These studies, which examined the variation in school performance after taking into account the background of the students in the schools, found that some schools do a better job than others in educating children, and the researchers have examined the characteristics of successful schools. However, as Willms (1998) points out, despite these findings, states and school districts continue to report misleading information about school performance by publishing overall average test scores, without taking into account the range of performance within a school.
Overall averages can be misleading because the variation in performance within schools is much greater than the variation among schools (Willms, 1998). That is, to take a hypothetical example, the difference between the performance of white students and black students in School A is much greater than the