Few researchers have addressed student achievement outcomes as a function of grade configurations for older elementary-aged students. Thus, this study was designed to determine differences between students' Grade 5 reading and mathematics achievement in elementary schools (K-5) as compared to intermediate schools (Grade 5, 5-6) for 5 academic years. Using archival statewide data, researchers used a rigorous five-step distance-based formula to match elementary schools to intermediate schools on four demographic/school characteristic variables. Students in K-5 settings attained statistically significantly higher levels of reading and mathematics achievement than did their counterparts, with moderate mean effect sizes of 0.37 and 0.47. (Contains 5 tables and 4 footnotes.)