Generalization is a fundamental cognitive process; however mechanisms of generalization early in development remain contested. According to one theoretical position, from very early in development conceptual information takes precedence over perceptual information. According to the alternative position, effects of conceptual knowledge have a protracted developmental course. The goal of the present research was to examine directly whether 3- to 5-year-old children privilege conceptual information over perceptual information. Participants were presented with triads of objects in which category membership conflicted with appearance similarity. Half of the children were first asked to sort pictures by category membership and then switch to sorting by similarity; the order of tasks was reversed for the other half of the children. A strong asymmetry in perseveration errors was observed across all three age groups: there was a marked decrease in accuracy when children were asked to switch form sorting by similarity to sorting by category membership, whereas the decrease was less pronounced when children were asked to switch from sorting by category membership to sorting by similarity (particularly for 4- and 5-year-old children who exhibited virtually no decrease in accuracy in the latter condition).