Some researchers argue that categorization in early development is knowledge-based rather than perceptually based. This approach requires young children to be able to attend to unobservable properties instead of perceptual features, which are usually more salient. However, potential immaturity of selective attention makes this possibility questionable. Current study tested both young children and adults with a match-to-sample task in which perceptual features were in conflict with the matching rule. Both behavioral and eye tracking data were collected. Eye-tracking results suggested that young children (3- and 4-year-olds) could not inhibit attention to the perceptual features, although behaviorally, 4-year-olds could. These findings are discussed with respect to theoretical accounts of category learning in early development.