This ex-post facto quantitative study examined how a comprehensive STEM education program impacts high school students' ACT math and science scores as well as their attitudes toward STEM. Using data from one STEM-designated school, the researcher examined ACT math, science, and STEM results for students who took the ACT in the Spring of 2024, using 8th-grade TCAP results as the covariate. The researcher ran an ANCOVA and linear regression analysis to answer four research questions about the impact of STEM course completion on students' ACT performance and attitudes. The findings show no statistically significant differences in ACT math scores between different levels of STEM courses (p =0.885), implying that the curriculum may not emphasize mathematical skills. However, there was a significant difference in ACT science scores based on the number of STEM courses (p = 0.044) completed, indicating that the STEM curriculum may improve students' knowledge of scientific concepts. Furthermore, the number of STEM courses completed did not predict students' attitudes toward STEM (p =0.214), although it did predict ACT STEM scores (p =0.041). This study addressed the benefits and limitations of STEM curriculum in fostering student attitudes and academic achievement regarding STEM. Future research recommendations include expanding the study to other STEM-designated schools and investigating the math curriculum inside STEM courses to improve educational outcomes. [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.]