Students with developmental disabilities and limited or no functional speech often use speech-generating devices. While the speech-output function of such devices is considered to have potential advantages, it is unclear whether the length of synthetic speech output influences augmented communication and natural speech production. To this end, we describe a two-phase study involving an adolescent with Klinefelter syndrome. In Phase 1, the frequency of augmented requests and natural speech were compared under three speech-output conditions (no-output, short-output, and long-output). In Phase 2, augmented requests in the long-output condition were no longer reinforced to determine if this would increase natural speech production. The presence and length of speech output did not influence the frequency of augmented requesting or natural speech production in Phase 1, but extinction of augmented requesting under the long-output condition in Phase 2 was associated with a significant increase in natural speech production under that condition, relative to the two other conditions. The implications of these findings for using speech-generating devices are discussed.