This study aims to validate a teacher-report measure of children's task-avoidant behavior, namely the Behavioral Strategy Rating Scale (BSRS), in a sample of 352 Finnish children. In each of the four waves from Kindergarten to Grade 2, teachers rated children's task-avoidant behavior using the BSRS, children completed reading and mathematics tests, and trained testers rated children's task-avoidant and social-dependent behavior after the test situation. Mothers also rated children's task-avoidant behavior in the last two waves. The results showed that a two-factor model including one factor representing task avoidance and one method factor accounting for wording effects among the negatively phrased items fitted the data best. The scale demonstrated strict measurement invariance across all four waves and satisfactory convergent and discriminant validity. Teacher-reported task avoidance was negatively associated with performance in reading and mathematics. The results suggest that the BSRS is a reliable, valid, and developmentally suitable instrument. (Contains 2 figures and 5 tables.)