The authors analyzed 44,664 annual measurements of forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) in 12,258 white children and 1,041 black children between 6 and 11 years of age in 6 communities. Sex and race-specific lung function development is described for the sample of preadolescent children. A simple model is presented for calculating percentiles of the distribution of FVC and FEV1 as a function of height, race, and sex. In a subset of children with at least 5 annual observations, observed growth was compared with the constant percentile curves (growth curves) of FVC and FEV1 given height, much as they track along growth curves of height given age, once the larger proportional measurement error of lung function is taken into account. The proposed growth curves can be applied clinically to evaluate a child's lung function, not only at a single examination but also longitudinally over a series of observations.