This research addresses the role of the level of conceptualization of categorical rules in the development of categorical flexibility in children. Experiment I and 2 compared categorical flexibility on three versions of a match-to-sample task differing in terms of a priori estimated levels of abstraction of the matching rules. Children aged between 3 and 8 were presented twice with a series of 4 picture sets (a target and 3 candidates for matching). Explicit instructions about the rule to be used before and after switching were given on each trial. It was found that age and conceptual difficulty of the rules both influence the extent of flexibility observed. Experiment 3 directly examined children's conceptualization of the matching rules at hand and revealed a developmental hierarchy similar to the one obtained in the flexibility task. Overall, the present findings suggest that categorical flexibility is the result of a successful top-down control which is modulated by children's representation of the categorical rules to be manipulated.