The goal of this study was to examine maternal support of spatial concept learning and planning at 36 months as predictors of children's math achievement at 4 1/2 years and first grade. Observational measures of videotaped mother-child interactions from the Boston site of the NICHD Study of Early Child Care and Youth Development (N = 140) were used to examine the effectiveness of support for spatial concept learning and planning during a block building play activity. Trained observers rated maternal support of children's learning of spatial concepts through spatial language and gestures, with higher ratings involving explanations and encouragement of children's use of spatial concepts. This measure was predictive of math achievement at 4 1/2 years when controlling for length of the parent-child observation, child gender, ethnicity, and IQ at 2 years, as well as maternal years of education, verbal intelligence, income-to-needs averaged from 1 to 36 months, parenting stress, general cognitive stimulation, and maternal support of numerical concepts during the same observation. Maternal support of children's planning skills, also rated by trained observers during the block building activity, involved identifying incremental steps to reach the block building goal, with higher ratings given for encouraging planning on the part of the child. This measure was predictive of math achievement at 4 1/2 years, as well as reading achievement at both 4 1/2 years and first grade, suggesting that maternal planning support has associations with the two key measures of school readiness, while maternal spatial support may be specific to mathematics. (author abstract)