What NAEP Can’t Tell Us About Charter School Effectiveness

By Jonathon Christensen & Lawrence Angel

Within a day of the release of the highly anticipated 2005 National Assessment of Educational Progress data in October, contending parties in the charter school debate had released claims that the findings supported their points of view. Meanwhile, we have continued to study the data to determine what conclusions can be drawn correctly. As it turns out, the claims from both sides overstate the extent to which determinations can be made about the effectiveness of the charter schools included in the sample.

The NAEP tests are part of an extensive effort undertaken by the National Center for Education Statistics to document the performance of America’s schools. NAEP data contain test results for a national sample of public and private school students in grades 4, 8, and 12; state-level samples include only public school students in these grades. The 2005 NAEP report draws on an impressive data set, containing math scores for 343,000 students and reading scores for 336,000 students from more than 17,600 schools nationwide.

The data are useful as an indication of how students are currently performing overall, both nationally and in each state. But they are much less useful as a tool for comparing the effectiveness of one type of school...