This study investigated the development of the many-to-one counting strategy in 4- year-old children. In the first experiment, 52 children participated. Their development with respect to two kinds of tasks, a hidden-items task and a needed-items task, was studied over four sessions. Children (n = 28) who accurately used the many-to-one strategy in Session 4 also participated in the second experiment. These children were presented with more difficult hidden- and needed-items tasks. It was found that children often produced the strategy for the first time on tasks with relatively few items. Most children then kept producing it, even if they initially did not obtain much profit from its use because of counting errors. Increasing task difficulty resulted in children making more counting errors or reverting to invalid strategies depending on the nature of the new task.