Background/Context: Previous literature has focused on mathematics socialization as it relates to the construction of mathematics identity, yet much of that research has been qualitative and lacking the theorization of high school Black girls. This study presents a longitudinal analysis of the relationships between socialization factors and mathematics identity among high school Black girls. Purpose/Objective/Research Question/Focus of Study: Mapping HSLS:09 variables onto Martin's (2000) theoretically rich Multilevel Framework for Analyzing Mathematics Socialization and Identity Among African-Americans, this study explored the distribution of high school Black girls' responses to questions that measure a mathematics socialization construct and identified relationships between mathematics socialization measures and mathematics identity for Black girls in their ninth- and eleventh-grade years of high school. Research Design, Data Collection, and Analysis: This quantitative study used secondary data from the base-year and first follow-up of the High School Longitudinal Study (HSLS:09), a nationally representative longitudinal study that started in 2009 with more than 23,000 ninth grade students from 944 schools. Using multiple linear regression in SPSS 26, the authors mapped HSLS:09 variables onto Martin's (2000) Multilevel Framework for Analyzing Mathematics Socialization and Identity Among African-Americans to test and examine the mathematics socialization constructs of high school Black girls who enrolled in a ninth-grade mathematics course (n=925) and continued participation in the HSLS:09 in their eleventh-grade year (n=637). Findings/Results: The results showed that Black girls in the ninth grade with higher scores on measures associated with Martin's theoretical framework (Sociohistorical, School and Institutional and the Intrapersonal subscales) were expected to have higher mathematics identity, after controlling for the other variables in the model. The Community and Family subscale did not contribute to the regression model. The strongest predictor in the ninth-grade year, the Intrapersonal subscale, was still a strong predictor of mathematics identity for Black girls in their eleventh-grade year (B = 0.16, t (636) = 20.244, p < 0.000). Martin's theoretical framework holds true for high school Black girls in relation to their mathematics identity, specifically their Intrapersonal socialization. Conclusions/Recommendations: The authors conclude that since mathematics is an exclusionary discipline and not necessarily designed for Black girls to succeed, understanding socialization factors can help the field of mathematics education design effective programming and teaching and learning experiences that disrupt hegemonic ways society has socially constructed mathematics. Specifically, mathematics teachers and other educators can work in solidarity with Black girls to help them increase their positive self-perceptions as mathematics learners. Educators engaging in these practices can support Black girls' resilience and agency in mathematics despite negative contextual factors.