We leveraged nationally representative data from the Panel study of Income Dynamics-Child Development Supplement (N = 3,562) and the Early Childhood Longitudinal study (N = 18,174), to chart the development of working memory, indexed via verbal forward and backward digit span task performance, from 3 to 19 years of age. Results revealed nonlinear growth patterns for forward and backward digit span tasks, with the most rapid growth occurring during childhood followed by a brief accelerated period of growth during early adolescence. We also found similar developmental trajectories on digit span task performance for males and females across the U.S. population. Together, this study highlights the relative importance of the childhood period for working memory development and provides researchers with a reference against which to compare the developmental changes of working memory in individual studies. From a practical perspective, clinicians and educators can also use this information to understand important periods of working memory growth using national developmental trends.