In elementary school, many children struggle in learning how to read. Some of these struggling readers will be identified to receive special education services as a student with a reading disability (RD), while other students will not be identified to receive such services but will continue to have low reading achievement (LRA). Limited research, however, has examined the differences in the longitudinal reading achievement trajectories between these two groups. Understanding the differences and similarities between children with RD and children with LRA is important for thinking about special education identification processes as well as prevention and intervention efforts. Therefore, the purpose of the current study was to compare the longitudinal reading trajectories of children with RD and children with LRA to determine whether the two groups had different reading achievement in the fall of kindergarten, different patterns of reading achievement from kindergarten through eighth grade, and different reading achievement outcomes in the spring of eighth grade. Primary analyses employed multiple group Latent Growth Modeling (LGM) to examine differences in the reading achievement trajectories between these two groups from kindergarten through eighth grade. Data were drawn from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-1999 (ECLS-K), which sampled approximately 21,410 children who entered kindergarten in 1998 and followed them through eighth grade. For children identified with RD or LRA between first and fifth grade (n = 1,080), LGM analyses revealed no significant differences between the groups in the fall of kindergarten, significantly different patterns of growth over time, and significant differences in their reading achievement in the spring of eighth grade, with the RD group outperforming the LRA group, even after controlling for gender, socioeconomic status (SES), race/ethnicity, and age. Findings highlight the importance of intervention and special education services to support the reading development of children who face challenges in learning to read. Additionally, findings point to the need for further research to identify why children with RD and LRA had different patterns of reading achievement over time, what the specific reading skill deficits of the students in each of these groups were, and how instruction and intervention can support students' reading development throughout their education. [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.]