Since the inception of the Common Core, school districts have sought to implement effective and fiscally responsible ways to support underperforming general education students. The need for supplemental assistance for struggling learners has emerged, particularly when tied to high-stakes testing. To offer appropriate assistance, school districts analyzed the possible ways through which they could support students and boost achievement. One popular method for providing intervention services and supplemental instruction is web-based learning. This study examined the effect of one particular supplemental web based program on student performance. It examined students who used the Castle Learning Online Program at a suburban high school in southern New York State, measured by Regents examinations and final course average. The study explores the explanatory valuables within the sample of students using Castle, such as gender and ethnicity. The results indicated that the use of the Castle program had a statistically significant impact on student performance as measured by New York State Regents examination scores and student final course averages. Furthermore, the results indicate a statistically significant impact in academic performance when controlling for gender and ethnicity. The results and empirical evidence outlined in this study, as well as the recommendations for practice provided in this dissertation, can assist school districts and school administrators in their decision making process regarding web-based programs and interventions for students. [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.]