Involvement in extracurricular groups is associated with positive outcomes for youth. Gender-Sexuality Alliances (GSAs) are school-based clubs that may provide benefits to sexual and gender minority (SGM) youth and their allies, yet little is known about what factors predict member retention. The current study explores individual- and group-level predictors of youth's sustained or discontinued membership in GSAs during a school year. Participants were 410 youth ( M age = 15.56; 83% sexual minority; 57% cisgender female; 70% White) and 50 advisors in 32 GSAs purposively sampled across Massachusetts who completed surveys at the beginning and end of the school year. Sexual minority youth and youth who took on more leadership roles at the beginning of the year were less likely to have left their GSA by the end of the school year. Youth who perceived higher levels of social support from their GSA trended less likely to leave their GSA as well, although the association was not significant. Youth who engaged in more advocacy were more likely to have left. Youth in GSAs with greater structure to their meetings were less likely to discontinue their membership; specifically, having a meeting agenda was uniquely predictive of member retention. Implications for GSA inclusivity and practices to promote retention within GSAs and similar social justice-oriented clubs are discussed.