The middle grades mathematics classroom is full of transitions that students must overcome to become successful long-term learners of mathematics. This transition can be exorbitantly more tumultuous for Black girls who must overcome gender and racial mathematics achievement stereotypes. Mathematics identities and achievement socialization trends can help Black girls navigate the challenges associated with these transitions. In this article, we argue that socializing agents can play a key role in the development of positive mathematics identities and positive achievement socialization patterns in Black girls. We use recent National Assessment of Educational Progress (NAEP) data to characterize Black girls' middle grades content knowledge through a strength-based and growth-oriented lens. Then using the data, we provide explicit examples of how parents, teachers, and curriculum developers acting as socializing agents can harness Black girls' funds of knowledge to address the observed challenges identified in the mathematics NAEP data.