Students who are not proficient in math are more likely to face negative long-term effects. In addition to adults with a lack of math skills facing a range of potential economic and mental health issues, the nation is also negatively impacted by a society of individuals who cannot contribute to the technological infrastructure. Project-based learning Science, Technology, Engineering, and Mathematics (STEM) curriculum programs have been developed for K-12 schools in response to the need to increase student mathematics achievement in the United States. One project-based STEM option is Project Lead the Way (PLTW), a non-profit organization that provides K-12 curriculum to school districts across the United States. This study aims to investigate the relationship between participation in PLTW high school engineering courses and mathematics achievement as measured by the PSAT/NMSQT Math Score. The study results suggest that project-based learning correlates with a significant increase in student mathematics learning. Exposure to project-based learning through participation in PLTW courses led to increased mathematics achievement when compared to no exposure to PLTW courses. Conversely, increased exposure to project-based learning in PLTW courses beyond the initial occurrence did not lead to further gains in mathematics learning. [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.]