Many elementary school students require and may benefit from supplemental reading support and interventions that can be provided by afterschool programs. The problem addressed in this study was that it was not known if third grade students benefited from an afterschool reading program in one East Tennessee District. The purpose of this quantitative study was to compare end of year scale scores on the Standardized Test for the Assessment of Reading (STAR) of third grade students who attended the afterschool reading program for 30 or more days and those who did not attend the afterschool reading program while controlling for beginning of year STAR scale scores. The theoretical framework for this quasi experimental ex post facto causal comparative design was Vygotsky's sociocultural and social development theory. This study involved a census sample of all third grade students enrolled in one school district during the 2016-2017, 2017-2018, and 2018-2019 school years, resulting in a total population of 373 students from four different elementary schools (232 attending the afterschool reading program and 141 not attending). ANCOVA results showed significantly higher end of year STAR scaled scores for students who attended the afterschool reading program compared to those who did not when controlling for beginning of year STAR scale scores (p < 0.001). The study's findings may contribute to positive social change by informing key stakeholders about the benefits of offering quality afterschool reading programs to all students, and as a result, afterschool programs could be harnessed as a means to improve students' reading achievement over time. [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.]