This study examined the functional independence of mand and tact operants in normally developing children and evaluated the role of SDs in demonstrating emergent responding. In Experiment 1, 4 children aged 4 to 5 years, were trained to mand or tact using left/right relations, then were tested for the emergence of the untaught tact/ mand operant. None of the participants demonstrated an emergence of the untaught operant under standard antecedent conditions. However, all of the participants demonstrated an emergence of the untaught operant when the SDs were modified. Experiment 2 replicated the work in Experiment 1, using 8 participants. The conditions were reversed according to ABAB reversal design methodology and counterbalanced across participants. The findings demonstrated the important role of antecedent variables in emergent responding.