This study investigated the relationship between working memory and early numeracy. It aimed to explore the possibility of training young children's working memory and to investigate the effects of such training both on working memory and on the specific domain of early numerical skills. Measures of working memory and numeracy were used with low-performing children in kindergarten. A total of 51 five-year-old children received one of two different versions of working memory training or no training at all. The two versions differed in the type of information the children were given to practice: non-numerical or numerical. After a pretest, 4 weeks of intervention took place, followed by a posttest. Children who participated in one of the working memory interventions significantly improved their working memory skills. Furthermore, their early numeracy skills also improved. Differences between both experimental conditions were small.