In this poem, the girl is clearly a good math student, since she does math problems in her head while she is at a swimming party. So "math scores" can refer to just the high marks she undoubtedly gets on her math exams. However, think about this girl's body. What kind of "math scores" could unfold in the air around her, as she is surrounded by boys? Could these be the measurements of her breasts, waist, and hips? At the end of the poem, the narrator makes reference to the bodies of the boys, their eyes, legs. and "the curve of their sexes" (19), so it would make sense for the poem to begin with the girl's measurements, creating a nice symmetry in the poem.