This study examined the influence of student-teacher relationships on children's anxiety and its differential association according to children's sex and academic achievement. The sample included 350 third- and fourth-grade students and their elementary school teachers. Results of multiple regression analysis indicated that student-teacher conflict at the beginning of the school year was associated with higher anxiety in students at the end of the year. The influence of conflict with teachers also varied for boys and girls, according to their academic achievement. Indeed, high-achieving girls reporting conflict with teachers presented more anxiety compared with boys and their low-achieving peers. This study highlights the influence of teachers on student anxiety, and brings attention to high-achieving girls, a group rarely considered at risk.