As federal mandates continue to emphasize the use of standardized tests, academic research is needed to determine if reading intervention programs are helping to close the achievement gap between struggling readers and their grade level peers. Although previous research indicated that reading intervention can be an effective tool for increasing students' reading achievement, what had yet to be determined is if a statistically significant difference existed between the change in pretest and posttest scores for READ 180 and non-READ 180 students, at one large suburban school district in southeastern Pennsylvania. This quantitative, causal-comparative study built on the theoretical foundations of Piaget and Vygotsky to understand how students learn, and used the Pennsylvania System of School Assessment and Group Reading Assessment and Diagnostic Evaluation to assess the effects of the READ 180 reading intervention program on student achievement. From a sample of 950 eighth grade students it was determined, using two Mann-Whitney U tests at the 0.05 significance level, that there was a statistically significant difference between students who received the intervention and students who did not. From this data, it can be concluded that there was a statistical difference between READ 180 and non-READ 180 PSSA scores (p = 0.00, U = 5966.5) and READ 180 and non-READ 180 GRADE scores (p = 0.017, U = 38026.5). As schools and districts continue to implement reading intervention programs to help struggling readers, understanding how these interventions effect student achievement on various standardized tests should be further investigated. [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.]