Several bodies of research have found different results with regard to presentation timing, categorization, and generalization. Both presenting instances at the "same time" (simultaneous) and presenting instances "apart in time" (spacing) have been shown to facilitate generalization. In this study, we resolved these results by examining simultaneous, massed, and spaced presentations in 2-year-old children's (N = 144) immediate and long-term performance on a novel noun generalization task. Results revealed that, when tested immediately, children in the simultaneous condition outperformed children in all other conditions. However, when tested after 15 min, children in the spaced condition outperformed children in all other conditions. Results are discussed in terms of how retrieval dynamics during learning affect abstraction, retention, and generalization across time. (Contains 4 figures.)