Schools that focus on science, technology, engineering, and mathematics (STEM) have been created to address a perceived need to increase numbers of students in the United States choosing and persisting in STEM career pathways. This study compared science programs in STEM and non-STEM high schools to determine how implementing a STEM design impacts science, a cornerstone of STEM. The multiple case study examined STEM integration, science instruction, and extracurricular opportunities in four high schools, two that were designated as STEM by the state's department of instruction and two that were comparable but did not have a focus on STEM. Results from this study indicate that STEM and non-STEM science programs are not significantly different in the schools studied. The two major differences that were found, greater incorporation of engineering design and increased access to extracurricular STEM activities, did not have beneficial impact on students' attitudes or career choices. Technology and math integration were similar but STEM schools integrated engineering design whereas non-STEM schools did not. Science instruction was similar. The numbers of observed inquiry-based lessons were similar, however, STEM schools had more project-based lessons, a form of inquiry-based instruction in which students create a product. A higher number of science-based extracurricular opportunities was available to students in STEM than non- STEM schools. This study offers important insight into the implementation of STEM education within existing school contexts and constraints. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]