Theory of mind describes the ability to engage in perspective-taking, infer mental states, and predict intentions, behavior, and actions in others. Theory of mind performance is associated with foundational cognitive and socioemotional skills, including verbal ability (receptive and expressive vocabulary), executive function (inhibitory control and working memory), and emotion knowledge. In a sample of 354 children from low-income households, theory of mind and foundational skills were directly assessed before and after kindergarten. Results indicate emotion knowledge, inhibitory control, and expressive language predicted improvement in theory of mind. Expressive language also served as a moderator such that children with low expressive language failed to improve in theory of mind regardless of initial theory of mind performance.