This work used mixed methods to understand the enrollment of historically underrepresented racial and ethnic groups in Science, Technology, Engineering and Mathematics (STEM) high schools. Grounded in previous work that described and recommended school practices for recruitment, admission, and retention of students from historically underrepresented racial and ethnic groups, this study analyzed data from the U.S. Census Bureau, New Jersey School Performance Reports, and a practitioner survey. The purpose was to describe the current state of racial and ethnic composition among enrolled students, and practitioner perspectives about recruitment methods, admissions practices, and retention strategies. The study found statistically significant under-enrollment of some racial-ethnic groups in STEM-specific high schools in New Jersey. The qualitative survey data identified methods to increase recruitment, admission, and retention strategies for students in historically underrepresented racial and ethnic groups. Recommendations were made to increase racial and ethnic diversity of students in STEM-specific high schools in NJ, which included but were not limited to including holistic admission criteria, counseling/mentoring programs, and programs to increase scientific identity and sense of belonging. The recommendations from this study may increase awareness about the degree of underrepresentation for particular racial and ethnic groups and inform practices in other schools to increase racial-ethnic diversity in STEM. The goal of this research is to investigate how to increase diversity in the STEM pipeline from high school to higher education, and ultimately increase diversity in STEM professions. [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.]