ObjectiveThis study aims to explore the reciprocal associations between personality traits (conscientiousness and openness to experience) and academic achievement in adolescents, using the Personality Achievement Saturation Hypothesis (PASH).BackgroundPersonality traits, especially conscientiousness, and openness, have been identified as strong predictors of academic achievement. The PASH provides a framework for understanding these relationships but has mainly been studied from a unidirectional perspective. This study extends the PASH to examine reciprocal associations and how they vary with different achievement indicators.MethodsUsing large‐scale panel data (N = 6482) of secondary school students in Germany, we applied cross‐lagged panel models and latent change score models to examine the differential reciprocal associations between personality traits (conscientiousness/openness) and academic achievement (school grades/achievement test scores) in language and math over two years from grades 7 to 9.ResultsIn line with the PASH, initial levels of conscientiousness were more strongly associated with school grades than with achievement test scores over two years. Simultaneously, prior school grades were more strongly associated with conscientiousness over two years. However, initial levels of openness did not show differential associations with either school grades or achievement test scores over two years. Similarly, prior school grades and achievement test scores were also not differentially associated with openness over two years.ConclusionsOur findings introduce an innovative lens through which we observe how the PASH can be leveraged to explain the differential reciprocal associations between conscientiousness and academic achievement. Further research is needed to examine if PASH could be similarly extended to disentangle the associations between openness and academic achievement.