School belonging can facilitate positive youth development and educational outcomes. Given that LGBTQ+ youth face marginalization in schools, there is a need to identify school supports that could still promote their sense of school belonging. We considered Gender-Sexuality Alliances (GSAs) as LGBTQ+ affirming school clubs. Among 92 LGBTQ+ student members of GSAs in nine states who completed weekly diary surveys over an 8-week period (M[subscript age] = 15.83 years, SD = 1.29; 50% youth of color; 51% trans or non-binary), we considered whether a youth's GSA experiences from meeting to meeting predicted their relative levels of school belonging in days following these meetings. There was significant within-individual (37%) and between-individual (63%) variability in youth's sense of school belonging during this time. Youth reported relatively higher school belonging on days following GSA meetings where they perceived greater group support (p = 0.04) and took on more leadership (p = 0.01). Furthermore, youth who, on average, reported greater advisor responsiveness (p = 0.01) and leadership (p = 0.01) in GSA meetings over the 8-week period reported greater school belonging than others. Findings showcase the dynamic variability in LGBTQ+ youth's sense of school belonging from week to week and carry implications for how schools and GSAs can support LGBTQ+ youth and sustain their ties to school.