Infants and children are avid learners. This constant aggregation of new knowledge, however, can interfere with past and future learning. Proactive interference (PI) occurs when past learning interferes with new learning, while retroactive interference (RI) is the attenuation of memory for previous learning as a result of new knowledge. Previous work has demonstrated that adults and children display PI and RI effects, but the developmental trajectories of these effects are less clear. The current study developed a new associative learning paradigm to concurrently test PI and RI in preschoolers and adults. Results demonstrated the presence of RI, and these effects were stable across age groups, suggesting that the mechanisms that modulate RI effects may already be mature in these age groups. No PI effects were found in either group, however. This surprising result suggests the role of associative complexity as a possible modulator of PI in these age groups.