Math performance became an increasing concern in the United States after the launch of Sputnik in 1957. This concern began with attempts to prescribe mathematical standards in the United States to improve student mathematics preparation. When the COVID pandemic began in 2020, policies on quarantining and remote learning were implemented, resulting in increased education gaps. The most contemporary NAEP report shows the first decline in math scores in the United States since the inception of the NAEP. Districts are looking for solutions. Districts are exploring intervention options, including Multi-Tiered Support Systems and Response to Intervention initiatives. They hope to reduce learning gaps, improve performance in math, reduce special education referrals, and provide more equitable access to advanced math courses. There is limited research on MTSS/RTI in mathematics at the secondary level. This study explores the implementation of one such intervention in the form of a supplemental math course offered to underperforming 9th-grade Algebra 1 students in the 2018-2019 school year in one New Jersey K-12 medium suburban district. Underperforming students scored below 750 on the 2017-2018 Math 8 PARCC score. There were three subsets of students in the study. The first subset was students who scored 750 or above on the Math 8 PARCC score and did not receive the intervention. The second subset of students scored under 750 and were offered the intervention but declined enrollment. The third subset was students who scored under 750 and enrolled in the intervention. The study examines the effect of the intervention on four dependent variables: Algebra 1 course grade, Algebra 1 New Jersey Student Learning Assessment (NJSLA), Geometry course grade, and the PSAT 10 math score. A multiple linear regression analysis was run for each dependent variable while controlling for predictor variables of intervention status, gender, race, special education status, free and reduced lunch status, the Math 8 course grade, and the Math 8 PARCC score. The study results revealed that the intervention course had no statistical significance influencing the dependent variables. While the intervention was statistically insignificant, the study offers new insight into applying these interventions. This research can help inform district decisions on implementing mathematics interventions and add to the body of research on mathematical interventions at the secondary level. [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.]