The purposes of this study were to evaluate the effects of an auditory-distractor stimulus and vocal-blocking task on performance on a math task and measures of overt verbal operants. College students served as participants, and they were instructed to solve an arithmetic problem while continuously emitting overt verbal behavior. The overt verbal behavior consisted of either talking aloud while solving the problem or reciting the alphabet. A third condition consisted of playing an auditory-distractor file containing the alphabet during the response interval while participants talked aloud. Data were collected on response accuracy, latency to respond, and frequency of echoic and self-echoic responses emitted during the response interval. The vocal-blocking task significantly affected performance on the math task when visual stimuli were absent. The decrease in performance coincided with significant decreases in participants' mean frequency of echoic and self-echoic responses. In sum, correctly responding to an arithmetic problem was significantly affected by the vocal-blocking task, indicating support for the necessity of verbal mediation during problem solving.