In this study we examined the effects of skill training, in particular mental abacus and music training, on working memory. Two groups of participants--children who had received mental abacus training and their controls--participated in Experiment 1. All participants performed the following span tasks: forward digit span, backward digit span, non-word span, operation span, simple spatial span, and complex spatial span tasks. Children (mean age: 12 years) who had received training exhibited greater simple spatial spans, but not other spans. In Experiment 2, the same span tests were given to groups of children (mean age: 12 years) and adults (mean age: 22 years) who had received music training and to their controls. For adults, the experimental group performed better than the control group with respect to both the digit span and non-word span tests. For children, the experimental group performed better than did the control group in all of the span tests. We discuss our results in terms of the domain-specific effects of skill training on working memory.