Student success in attaining college acceptance, gaining scholarship(s), and having postsecondary education or workforce choice is closely tied to achievement on the most widely used and accepted college entrance examination, the "ACT". Researchers have studied various interventions designed to impact "ACT" scores, but one noticeable gap in research was with long term, curricular intervention provided during the school day and available to all students. The purpose of this study was to investigate the impact of an "ACT" mathematics course offered for 18 weeks during the school day. A sample of 36 participants from a suburban high school in the southeast was drawn from students whose "PLAN" (preliminary "ACT" test for 10th graders) scores predicted that they would not meet the college readiness benchmark on the "ACT". In a quasi-experimental design, students were matched on gender, ethnicity, and "PLAN" score range and were placed into a control or treatment group. Both groups were enrolled in the next mathematics course in their sequence but only the treatment group was also enrolled in the intervention course. The research questions focused on four areas. Were there significant differences in the treatment group scores after taking the intervention course? Were there significant differences in the scores of the control group and the treatment group? Were there significant differences in reaching the college readiness benchmark and in score changes among ethnicity groups? Were there significant differences in score changes among students whose pretest score ranges were different? The intervention course made a significant impact on the participants' posttest scores on the "ACT" mathematics test. The participants within the "PLAN" range of 17-18 on the pretest had the most gains. Participants who achieved the college readiness benchmark in mathematics were in the 17-18 "PLAN" range and also received intervention. Ethnicity did not have a significant impact on score changes. Major implications are that intervention can impact "ACT" scores, educators should consider early high school intervention, intervention makes more impact than ethnicity, and school districts should consider priority for staffing and scheduling "ACT" intervention courses so that all students have a fair chance to maximize scores and, thus, future educational options. [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.]