This study investigated the development of children's knowledge of many-to-one counting. Four-year-olds (n=51) either participated in a training or in a control group. The training taught children how to allot Y physically not present items to each of X objects and how to count these items in the process. It was found that most children could be taught how to perform a many-to-one count. Counting performance was related to insight into the concept of multiplication. More specifically, learning of the many-to-one strategy was related to a better insight into aggregation over sets of items.