It has been suggested that individuals’ achievement-related beliefs and attitudes play an important role in academic environments. This paper examines first, the cross-lagged relations between kindergarteners’ task motivation and performance in mathematic skills and literacy, and second, the lagged relationships between task motivation, self-concept of ability, and performance in mathematics and reading. In Study 1 children (n = 139) were assessed twice during their preschool year. The results showed that only math-related task motivation and mathematic performance showed cross-lagged associations with high motivation leading to better performance, and better performance leading to high motivation. In Study 2 longitudinal data were gathered from 216 students between Grade 1 and Grade 7 with yearly assessments. Both reading and math performance were found to predict the students’ subsequent self-concept of ability. In addition, academic performance predicted subsequent task motivation, and self-concept of ability mediated the impact of academic performance on task motivation. In both studies the results were mostly similar for boys and girls.