This study investigates whether the use of a spacing strategy absolutely improves final performance, even when the learner had chosen, metacognitively, to mass. After making judgments of learning, adult and child participants chose to mass or space their study of word pairs. However, 1/3 of their choices were dishonored. That is, they were forced to mass after having chosen to space and forced to space after having chosen to mass. Results showed that the spacing effect obtained for both adults and children when choices were honored. However, using a spacing strategy when it was in disagreement with the participant's own choice, or forced, did not enhance performance for the adults (Experiment 1). And although performance was enhanced for the children (beyond massing strategies), it was not as good as when the spacing decisions were self-chosen (Experiment 2). The data suggest that although spacing is an effective strategy for learning, it is not universal, particularly when the strategy is not chosen by the learner. In short, metacognitive control is often crucial and should be honored. (PsycINFO Database Record (c) 2009 APA, all rights reserved).