Between- and within-family changes in 4 dimensions of parent involvement in children's learning were examined from prekindergarten to kindergarten and from kindergarten to first grade. Children's literacy, language, and mathematics skills were individually assessed at prekindergarten entry and end of first grade. Parents' provision of cognitive stimulation decreased overall from prekindergarten to kindergarten (d = -0.26) and from kindergarten to first grade (d = -0.53), and variety of out-of-home experiences increased from kindergarten to first grade (d = 0.30). A substantial percentage of the sample increased or decreased their participation in home-based or school-based activities. The degree of change in parent provision of cognitive stimulation from kindergarten to first grade and variety of out-of-home experiences from prekindergarten to kindergarten predicted children's first-grade mathematics skills. Increases in home learning resources from prekindergarten to kindergarten were associated with higher first-grade mathematics outcomes of children with lower prekindergarten-entry mathematics skills. (Contains 1 figure, 3 tables, and 1 note.)