Preschool children vary in their numerical knowledge, and this variation predicts math achievement throughout elementary school. Can preschool interventions that exercise school-relevant numerical concepts support later school math learning, and if so, what numerical activities should be targeted to best foster this learning? Here we ask whether a game-based intervention targeting preschool children’s understanding of the base-10 compositional system of number words and symbols improves their school-relevant numerical concepts in the short term. Five- to six-year-old children who played a numerical board game at home with their parents for two-three weeks showed improved preschool numerical concepts, compared to children who played a game with similar materials and procedures but no numerical content. This finding takes a first step toward developing and evaluating a suite of game-based interventions, leveraging research in developmental cognitive science both to enhance children’s learning in school and to deepen understanding of how children learn.