Although intelligence and personality traits have long been recognized as key predictors of students' academic achievement, little is known about their longitudinal and reciprocal associations. Here, we charted the developmental interplay of intelligence, personality (Big Five) and academic achievement in 3880 German secondary school students, who were assessed four times between the ages 11 and 14 years (i.e., in grades 5, 6, 7, and 8). We fitted random intercept cross-lagged panel models (RI-CLPs) to investigate reciprocal within-person associations between (a) academic achievement and intelligence, (b) academic achievement and personality, as well as (c) intelligence and personality. The results revealed negative within-person associations between Conscientiousness and Extraversion assessed at the first wave of measurement and intelligence assessed at the second wave. None of the reciprocal personality-achievement associations attained statistical significance. Academic achievement and intelligence showed reciprocal within-person relations, with the strongest coefficients found for achievement longitudinally predicting intelligence. Our work contributes to developmental theorizing on interrelations between personality, intelligence, and academic achievement, as well as to within-person conceptualizations in personality research.