This mixed-methods study approach investigated the impact of standardized tests on student achievement from the STEM program and the traditional program in a suburban high school. Qualitative data were collected from interviews, focus groups, and questionnaires to get perceptual data from teachers. Quantitative data were collected from different demographic information and the standardized tests American College Testing (ACT) and end-of-course examination (EOC). An independent sample "t" test, the Chi-Square Test of Independence and Pearson R Correlation of association test were used to analyze the data collected. Documents with the graduation rates for the participants were reviewed, and both programs had a 100% graduation rate. The results of the survey were presented in tables and figures and then interpreted using the results of the statistical tests. Results from this study showed there was no statistically significant difference in the mean average for ACT, Biology, Math I and English II scores. This led to the conclusion that there were no statistically significant differences in the achievement and graduation rate of students who were in STEM and traditional programs. The results for ACT, Biology, and Math 1 favored the STEM students; while the results for English II favored the traditional students. The qualitative data from teachers who were surveyed and those who participated in the focus groups and individual teacher interviews showed there was an association in student achievement based on the professional development activities in which the STEM teachers participated. Also, the participating teachers had a positive perception regarding the overall impact of the STEM program. The study showed the rigorous and challenging STEM curriculum increased motivation, engagement, achievement, and self-efficacy among the STEM students. Staff development and in-service training for the STEM teachers led to teacher self-efficacy and equipped them with the ability to instruct and facilitate instructions in STEM classrooms effectively. [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.]