The purpose of this study was to investigate developmental gender differences in academic achievement areas, with the primary focus on writing, using the child and adolescent portion (ages 6-21 years) of the "Kaufman Test of Educational Achievement-Second Edition, Brief Form," norming sample (N = 1,574). Path analytic models with gender, parent education, age, age[superscript2], and gender-by-age moderation as predictors of reading, writing, and math were used to test for gender differences and for the influence of development on these differences. A small but consistent advantage was identified for females in reading. No gender differences were detected in math. The most important results of the present study pertain to a gender gap in writing in favor of females that increased as a function of age. Male students are at greater risk for writing failure than are females.