The purpose of this study was to examine the effects of three basic demographic variables on reading test scores for students in the middle elementary grades. Limited English proficiency (LEP), race/ethnicity and socio-economic status (SES) were studied to determine their influence individually and in combination on performance in large-scale assessment programs. Two data sets were analyzed: 1. Grade 4 reading results for the 2003 National Assessment of Educational Progress (NAEP) and 2. Grades 3 and 5 reading results for the 2003 Minnesota Comprehensive Assessment (MCA). The NAEP data contains results for over 179,000 students and the MCA data files consist of results for approximately 60,000 students at each grade level. The NAEP results were analyzed both for the overall national public school sample and for the 50 state-level jurisdictions. The overall NAEP results indicate that all three variables have a significant effect upon reading scores. There are large "gaps" in average test scores among racial/ethnic groups, LEP and Non-LEP students and students eligible and not eligible for the federal free and reduced lunch program. The joint effect of the variables is shown by the fact that the racial/ethnic gaps are dramatically reduced when students are cross-classified by SES and LEP status. The state-level NAEP data reveal a pattern of strong negative correlations between the percent of students in each state eligible for free and reduced lunches and mean state NAEP scores. A similar pattern was observed in the correlation of percent of students classified as LEP for Hispanic and Asian student mean scores. The MCA data showed results parallel to the NAEP data. The gaps between White and Hispanic and White and Asian students were shown to be largely attributable to the incidence of LEP students in the two minority groups. Our analyses clearly demonstrate that reports of "achievement gaps" in assessment results are misleading if SES and LEP status are not taken into consideration. Appended is: Description of NAEP Reading Assessment. (Contains 1 note, 17 figures, and 8 tables.)