The purpose of this study was to investigate the information regarding the comparative relationship between the proficient mathematics scores of eighth-grade students on the 2009 state mathematics assessments and the 2009 National Assessment of Educational Progress (NAEP) mathematics assessment by state, census-defined regions and AYP subgroups. Analysis was completed and six research questions were used to guide the study. A multiple regression was used to assess the relationship between the percentage of eighth-grade students who were proficient in mathematics as assessed by the 2009 NAEP and those who were proficient in mathematics as assessed by their 2009 state assessment. A significant quadratic (non-linear) relationship between the state and NAEP levels of proficiency was determined. Several two-factor split plot (one within-subjects factor and one between-subjects factor) analysis of variance (ANOVA) were conducted to determine if region moderated the difference between the percentage proficient on the state and NAEP assessments for eighth grade students overall and in the following AYP subgroups : (a) low socioeconomic students, (b) white students, (c) black students and (d) Hispanic students. The within-subjects factor was type of test (NAEP or state), and the between-subjects factor was region (Midwest, Northeast, West, and South). Overall, the percentage proficient on state mathematical assessments was always higher than the percentage proficient on the NAEP mathematics assessments. The degree of discrepancy is discussed, as well as possible reasons for this divergence of scores.