Previous research on the acquisition of verbal behavior in children with developmental disabilities has focused on teaching four primary verbal operants: (1) "mand"; (2) "tact"; (3) "echoic"; and (4) "intraverbal". In Skinner's (1957) analysis of verbal behavior, he stated that each verbal operant is maintained by unique antecedent and consequence events and, therefore, is functionally independent. Skinner's work served as a catalyst for a growing body of literature that has evaluated the functional independence of verbal operants and the emergence of untrained verbal operants. This paper describes recent studies that have evaluated the functional independence of verbal operants. Procedures that facilitate the emergence of untrained verbal operants and important areas of future research to increase efficiency of language programs for children diagnosed with developmental disabilities are discussed.