Rett syndrome (RTT) is associated with a range of serious neurodevelopmental consequences including severe impairments in communication. Currently, no evidence-based communication interventions exist for the population (Sigafoos et al., 2009), and there is limited empirical evidence that individuals with RTT are able to demonstrate operant motor behaviors, (e.g., behaviors that are controlled by the individual in order to create an effect on the environment). The purpose of the current study was to examine the effectiveness of functional assessment (FA) and functional communication training (FCT) methods for teaching a clinical case series of girls and women (aged 4-47 years) with classic RTT to request preferred events or items using an augmentative communication device. Functional analysis (FA) was used to identify the communicative function of potential communicative acts (PCAs) identified during parent interviews and observations. Subsequently, each participant was taught to activate a voice-output switch to request the functional reinforcer identified in the FA. Using ABA and ABAB single case experimental designs, the degree to which each participant alternated between the PCA and switch activation according to changes in the environmental consequences (e.g., reinforcement vs. extinction for a particular response) was examined. Clear experimental effects of the intervention condition were observed on at least one response for six of the seven participants. The remaining participant did not complete the study. Overall, these results suggest that individuals with RTT can use intentional motor behaviors, and are responsive to environmental consequences. These results have important implications for the development of appropriate communication interventions for this population.