Low-income children often enter kindergarten behind higher-income peers in math; gaps also exist in social-emotional aspects of school readiness, fueling interest in cross-domain relations and whether -- and which -- social skills matter for promoting early math skills. With a sample (N = 76) of mostly low-income, minority preschool children, we investigated the extent to which children's adaptive social problem-solving skills at preschool entry vary and whether these differences moderate early math skill development during the preschool year. Using longitudinal modeling, results show that children begin preschool with varying adaptive social problem-solving skills; these variations are associated with differences in the rates at which children learn early math skills, controlling for baseline language and age. Findings illustrate an increase in the math gap associated with differences in baseline adaptive social problem-solving skills, suggesting that low-income children with more adaptive social problem-solving skills -- already present at preschool entry -- learn early math skills faster compared to peers with fewer adaptive social problem-solving skills. Results can guide preschool curricula in programs serving low-income children.