To examine the cross-lagged relationships between children's task motivation in mathematics and literacy, and their related performance, 139 children aged 5–6 years were examined twice during their kindergarten year. The results showed that only math-related task motivation and arithmetic performance showed cross-lagged relationship: the higher the math-related task motivation children reported in the beginning of the kindergarten year the higher the level of their arithmetic performance at the end of the kindergarten year. Moreover, the higher the level of children's arithmetic performance the more the interest in mathematics children reported later on. Literacy-related task motivation and literacy performance did not show a similar pattern of relations.