Growth in Test of Cognitive Skills (TCS) scores and Comprehensive Tests of Basic Skills (CTBS) reading, math, and total achievement scores from 3rd to 10th grade was studied in 328 public school students in a middle-class suburban community. Surprisingly, groups differing in ability and achievement in 3rd grade made parallel progress over time, and some "fan-close" effects were found. With growth curve analysis of individual students using hierarchical linear models, initial status on cognitive ability predicted initial achievement scores but did not affect the rate of growth. Similarly, initial status in achievement predicted the intercept but not the slope in cognitive ability scores over time. Although replication is needed, this study illustrates how districts could use standardized test data to document growth of academic skills over time in high-, middle-, and low-achieving children: in racial or socioeconomic status subgroups; or in different classrooms, schools, or districts.