--- - |2+ Background Research reveals longitudinal bidirectional associations between changes in academic achievement and psychopathological symptoms. However, little is known about developmental changes in the magnitude of these associations, from childhood to adolescence. Methods Participants were 648 Chinese children (347 males) who were followed from Grade 5 (mean age: 11.18 years) to Grade 9. Academic achievement and two types of symptoms (externalizing, depressive) were assessed annually. Structural equation modeling was used to examine longitudinal bidirectional associations between achievement and psychopathological symptoms, and developmental changes in effect sizes. Models were estimated using cross‐lagged panel modeling (CLPM), as well as random intercepts cross‐lagged panel modeling (RI‐CLPM). Results The data supported the hypothesized academic incompetence and adjustment erosion effects, as well as the hypothesized developmental change in the academic incompetence effect whereby prior achievement's effects on subsequent externalizing increased with age. Results were similar for both genders and unaffected by inclusion of common risk factors as covariates. Conclusions There are bidirectional associations between symptoms and achievement that change markedly across the transition into adolescence. Interpreting the effects using a developmental perspective, changes in reciprocal effects may be dynamic. The findings suggest that targeting both psychopathology and low academic achievement is worthwhile, but that distinct treatment effects will be found in childhood versus adolescence. - Journal of Child Psychology and Psychiatry, EarlyView.