At the 3-year laboratory visit, children were administered the Dimensional Change Card Sort (DCCS; Zelazo, 2006) task, a standard procedure for assessing cognitive flexibility in young children. Children were asked to sort 12 bivalent test cards (e.g., blue cars and red flowers) into 1 of 2 bins marked by bivalent target cards that each match the test cards on a single dimension (i.e., blue flowers and red cars). On pre-switch trials, children were instructed to sort 6 cards according to one dimension (e.g., color). Then the sorting rules changed, and children were instructed to sort another 6 cards (identical to the previous 6) according to the other dimension (e.g., shape). The order of sorting dimension was counter-balanced across participants. Only children who sorted at least 4 of 6 pre-switch cards correctly were administered post-switch trials.
