Background: When exposed to evaluative situations, up to 40% of students develop test anxiety, reflected, namely, by extensive worry, intrusive thoughts, and physiological arousal. Though the negative influence of test anxiety on later school performance is well documented, the role of students' initial achievement in the development of later test anxiety is less clear. Aims and Sample: To better capture the nature of the relations between prior mathematics and language arts achievement and later test anxiety across genders, this study examined linear and curvilinear relationships among 1,569 French-speaking Canadian students followed across the transition to secondary school, a critical period for test anxiety. Methods: Students completed a questionnaire at the beginning and the end of the first year of secondary school, and schools provided us with students grades at the end of 6th grade and the fall of 7th grade. Results: Multilevel regression analyses showed that only mathematics achievement at the end of elementary school predicted test anxiety at the beginning of secondary school. In secondary school, beginning-of-year achievement in both mathematics and language arts predicted test anxiety at the end of this same year, but different patterns were observed for boys and girls. Conclusions: Because nonlinear relations were observed at each timepoint, low achievers may not be the only group of students who are at greater risk of developing high levels of test anxiety. Therefore, interventions targeting students with different achievement profiles might help to reduce test anxiety and facilitate the transition to secondary school.