This longitudinal quantitative study compared literacy achievement of students from second through sixth grade based on two organizational systems: graded (traditional) and nongraded (multiage) classrooms. The California Standards Test (CST) scaled and proficiency scores for English-Language Arts (ELA) were used as the study's independent variable to measure student performance. A matched control was utilized in which nongraded students were compared with graded students based on gender, ethnicity, and date of birth. Data analysis included independent samples t-test, analysis of variance (ANOVA), and effect size. Results showed that nongraded students had a significant advantage over their graded counterparts in literacy achievement (p=0.000). Effect size for the matched group increased with length of exposure in the nongraded program from Cohen's d=0.49 to d=0.99. It is difficult to determine if significant outcomes were the result of classroom structure or instructional strategies used in the nongraded setting. However, a unique quality of this study involves the rare conditions and matched control design that allowed for variables to be controlled, which have yet to be simultaneously accounted for in multiage studies to date. Based on the results, this study suggested that nongraded education, by responding to the developmental nature of children in the classroom, may offer a viable alternative to the graded system. In nations such as Australia, New Zealand, Netherlands, Finland, and Canada with the highest literacy rates in the world, nongraded classrooms are common educational practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]