Effective and equitable CS [computer science] teaching is contingent on teachers' robust understanding of equity issues in CS classrooms. To this end, this study examined high school teachers' perceptions of equity during their participation in a CS teacher certificate program over two years. The participants are from various disciplines and from schools that serve under-represented students. Using a qualitative approach, we conducted content analysis of the teachers' written reflections and responses to semi-structured interviews. Based on the justice-centered framework, we analyzed the major themes that emerged from the content analysis. The findings provide insights into high school CS teachers' understanding of equity, the strategies that teachers use to address equity issues, and how teachers interpret the causes of inequities in CS classrooms. This research presents frameworks for examining teachers' conceptualizations of equity and can inform the implementation of future professional development programs for CS teachers.