U.S. non-profit organizations (NPOs) offering Science, Technology, Engineering, and Mathematics (STEM) programming, particularly those serving minorities and women, are becoming guideposts that assist academic, government and corporate institutions alike to steer their efforts and investments towards achieving their diversity and inclusion goals. Despite multi-year, multi-billion, and multi-resource investments in broadening STEM access and inclusion, the inequitable representation of young women and girls of color actively participating in school and out-of-school STEM programs continues to persist. The primary aim of this study was to validate a feminist theoretical framework grounded on the constructs of intersectionality, collective impact, and accountability systems, to help inform and disrupt persistent trends for women graduating in engineering and computer science through the third sector's facilitation of STEM programming. A secondary objective was to understand the history and trajectory of the change and emergence of non-profit STEM Girl-Centered Organizations (SGCOs) and their profiles as a comparative measure of their relative status within the third sector ecosystem, how they serve, and who they serve. By leveraging over twenty-five years of practical experience and applying a mixed-methods research methodology, the research findings pointed to 1) an early adoption of intersectionality concepts into program outreach efforts by integrating cross-elements of race/ethnicity, geographies, and socioeconomic markers of identity; 2) emerging interest in, and incorporation of, culturally responsive programming that is better matched to the needs of diverse program beneficiaries; 3) an increase in equitable program access for participants residing in under-resourced communities; 4) a growing appreciation for the value of partnerships as a precursor to more authentic collective impact collaborations; and 5) priority shifts in systems of accountability from funders to primary programs' beneficiaries. [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.]