In education, relative age effects (RAE) are present if a student's age when compared to that of his/her classmates has implications for scores on measures of achievement and performance. Researchers studying relative age have established significant, but inconsistent effects of being relatively older or younger in a grade level on measures of achievement. Test results are used to identify students' needs for educational services and interventions, and the effects of relative age could influence a student's access to these academic supports. This study used the Early Childhood Longitudinal Study, Kindergarten Class of 2010-11 (ECLS-K:2011) dataset to investigate the strength and persistence of relative age effects on achievement assessments and teacher observations of student behavior in elementary school. I used an instrumental variable (IV) of the student's predicted relative age to isolate the exogenous effects of students' relative age. I integrated the IV into an autoregressive cross-lagged pathway to model the direct, indirect, and total effects of relative age on students' academic achievement, teacher ratings of students' academic performances, and teacher ratings of students' learning behaviors. I identified an attenuation in the direct effects of relative age on students' achievement and teacher ratings of students' learning behaviors by the end of third grade. Further examination of the data revealed a decrease in the total effect of relative age on students' achievement by the end of third grade, but a sustained total effect of relative age on teacher ratings of students' academic performance and learning behaviors from kindergarten through third grade. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]