In 1998 and again in 2002, samples of eighth grade students in California were tested in reading as part of the state-level component of the National Assessment of Educational Progress (NAEP). In each of these years, all eighth graders in the state were also required to participate in the state's accountability testing, which included the reading test in the Stanford Achievement Tests, Ninth Edition (SAT 9). State-level comparisons of performance on these two assessments showed improvement in the SAT 9, but a slight decline on NAEP (not statistically significant). To examine whether this trend discrepancy might be attributable to content differences between the two tests, SAT 9 reading items were coded into categories corresponding to the NAEP content strands plus a category for items not aligned to the NAEP framework. Analyses of performance within strands indicate that content differences probably cannot explain the discrepant trends on the state accountability test versus NAEP, although differences related to item format are a strong possibility. Implications and alternative explanations are discussed. (Contains 7 endnotes, 6 tables, and 10 figures.)