This study compared the involvement of American and Chinese mothers in their 5- and 7-year-old children's number learning in their everyday experience and during mother-child interaction on mathematics tasks pertaining to proportional reasoning. Results indicated that Chinese mothers of both the 5- and 7-year-old children were more likely to teach mathematics calculation in their everyday involvement with children's number learning than their American counterparts. No differences were found in maternal instruction between American and Chinese mothers during the mother-child interaction on mathematics tasks. However, maternal instruction was related to Chinese children's learning of proportional reasoning but negligibly related to American children's learning of proportional reasoning.