The purpose of this study was to determine whether age differences affect students' academic achievement, and whether age differences affect students in low-income areas differently than those in mixed or higher-income areas. Student achievement data for grades 3, 7, and 11 in language arts and math were obtained from a variety of schools located in an economically diverse region of central California. Results of Multivariate Analysis of Variance (MANOVA) suggest that age-related differences contribute only minimally to the differences in academic achievement, and that youngest students' academic performance is nearly equal to or actually better than that of the oldest and overage students (those who entered kindergarten a year later, repeated kindergarten or were retained in a later grade) as they progress through the educational system. [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.]