This study examined the effectiveness of an ACT intervention course developed for high school juniors at Anderson County High School during the 2011-2012 school year. This study compared the ACT composite test scores of the treatment group to the ACT composite test scores of the control group by using their PLAN scores as a baseline, to determine if there was an increase in the ACT composite scores of the treatment group. The relationship between the upper division English and math courses a student completed by the end of the junior year, a student's grade point average, and their ACT composite scores also was examined. The intervention studied was a yearlong ACT test preparation course taught during a 30-minute enrichment block four days a week for 30 weeks during the 2011-2012 school year. The sample consisted of 168 students in the control group and 165 students in the treatment group. Ten null hypotheses were tested using a paired samples t-test, independent samples t-test, and a Pearson r correlation. Six of the null hypotheses were rejected and four were retained. Results of the study indicated that students who were below the college and career benchmarks on the PLAN test were still below the college and career benchmarks on the ACT test, even with the ACT test preparation course. The treatment group's math portion of the ACT sub-test scores saw the largest growth, just over one point. Science and English sub-test scores showed the least growth. The study determined there was a statistically significant relationship between the level of math and English courses taken by a student in high school and their ACT scores. The study also determined there was a statistically significant relationship between a student's ACT composite score and a student's GPA. In the study female students on average out scored male students by more than one point on the ACT composite score. It is recommended this study be replicated in an urban school system to provide evidence on the validity of the study. [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.]