This study examined the dynamics between perceptions of mathematics task-orientation and mathematics performance among Finnish adolescents over a period of two last years of secondary school. Task-orientation in math was assessed at the beginning of grade 8 and again at the end of grade 9 using both student and teacher reports. At the same time points, students' mathematics performance was evaluated via standardized test. The cross-lagged associations of task-orientation and mathematics performance were examined taking account the possible impacts of general cognitive ability, technical reading skills, reading comprehension and gender. The results showed that a high level of mathematics performance in the beginning of 8th grade positively influenced student-rated task orientation at the end of secondary school. In turn, the anticipated reciprocal relationship between task orientation and mathematics manifested particularly in the model with teacher-rated task orientation. Implications for practice are discussed.