Previous research suggests that experimenter-induced labeling of test cards improves preschoolers' performance on the Dimensional Change Card Sort Task (DCCS), a measure of flexible rule use. Three experiments attempted to further clarify how labeling aids performance on the DCCS. Experiment 1 examined the nature of the labeling effect but failed to show any benefit of labeling on children's performance. Experiment 2 failed to replicate the labeling effect reported by [Kirkham, N. Z., Cruess, L. M., & Diamond, A. (2003). "Helping children apply their knowledge to their behavior on a dimension-switching task." "Developmental Science, 6", 449-467] despite closely matching their procedures. Experiment 3 demonstrated that labeling procedures designed to counteract the suppression of the post-switch sorting dimension also failed to improve performance on the DCCS. We discuss the implications of these findings for identifying factors that positively affect preschoolers' cognitive flexibility. (Contains 1 table.)