The present study investigated the extent to which mothers' support for their children's sense of competence, autonomy and relatedness predicts their children's interest in math and reading, and also their mastery orientation, during the transition to primary school. One hundred fifty-two children were examined twice during their first grade year regarding their interests and mastery orientation (Time 1 and Time 2). Mothers filled in a diary and questionnaire measuring maternal support, also on two occasions (Time 1 and Time 2). Children's school performance in reading and math was tested at the beginning of the first grade (Time 1). The results showed that, after controlling for the autoregressor and level of performance, all of the maternal support variables predicted children's subsequent interest in mathematics but not in reading. Children's mastery orientation, in turn, was only predicted by mothers' support for autonomy. (Contains 1 table and 1 figure.)