Despite expansion in K-12 computer science education (CSEd), student access and participation remain stratified. This study examines how participation in a Texas-based Research-Practice Partnership (RPP) impacted teachers’ capacity to affect students’ access to, participation in, and experience of CSEd. Eighteen teachers (59% Black or African American, 19% Hispanic or Latino, and 70% women) participated in this study while engaging in a comprehensive professional development (PD) that included content knowledge training, inclusive pedagogy courses, and collaborative workshops. Data collection occurred after two years in the three-year program through semi-structured interviews, analyzed using thematic analysis combining deductive coding based on the CAPE framework (Capacity, Access, Participation, Experience) with inductive pattern identification. Findings reveal ways in which expansion in teacher capacity due to the RPP helped teachers expand conceptions of access beyond course availability to address systemic barriers through intentional recruitment and pipeline creation; developed specific strategies ensuring diverse participation by monitoring classroom demographics and using varied participation methods; and created culturally relevant experiences by integrating students’ lived contexts and leveraging the participants own authentic identities as pedagogy. This research demonstrates how RPPs develop teachers’ capacity through sustained and culturally relevant PD, revealing that initial awareness of stratification translates into teaching practices with appropriate scaffolding and time, ultimately fostering learning environments where all students can thrive in CSEd.