The "testing effect" refers to the striking phenomenon that repeated retrieval practice is one of the most effective learning strategies, and certainly more advantageous for long-term learning, than additional restudying of the same information. How retrieval can boost the retention of memories is still without unanimous explanation. In 3 experiments, focusing on the reaction time (RT) of retrieval, we showed that RT of retrieval during retrieval practice followed a power function speed up that typically characterizes automaticity and skill learning. More important, it was found that the measure of goodness of fit to this power function was associated with long-term recall success. Here we suggest that the automatization of retrieval is an explanatory component of the testing effect. As a consequence, retrieval-based learning has the properties characteristic of skill learning: diminishing involvement of attentional processes, faster processing, resistance to interference effects, and lower forgetting rate.