This study (N 196) examined the extent to which the frequency of parent–child math activities in preschool was associated with children’s developmental trajectories of math skills from preschool to primary school. Parents reported the frequency of their involvement in a variety of math activities with their preschool children. Children were tested individually on their formal (i.e., math knowledge that involves verbal or written symbolism, such as rote counting and written computation) and informal (i.e., object-based numeration and operations, such as number line concepts and object-based calculation) math skills from preschool to first grade. The results showed that the frequency of parent–child formal math activities, including number skill and book activities, was not associated with children’s formal or informal math trajectories. In contrast, the frequency of informal math activities, including number game and application activities, was associated with formal math skill levels in preschool. More important, parental involvement in application activities in preschool significantly predicted the rate of growth in formal math skills through first grade. This predictive relation persisted after controlling for the other three types of math activities and other child- and family-level variables. The findings underscore the importance of early parent–child application activities in engendering possible long-term effects on children’s math skill development.