We evaluated the effects of behavioral skills training on improving participant implementation of functional communication training with multiple schedules when working with a confederate. Behavioral skills training produced mastery-level responding for all six participants who required training, providing the first empirically supported training for this functional communication training approach. Next, we assessed durability during training challenges with (a) procedural changes to the original protocol, (b) a novel confederate with different discriminative stimuli and reinforcers, and (c) relapsed confederate destructive behavior. Training effects degraded at least once for all participants and in 62% of training challenges, although continuing to expose the participant to the challenging situations or providing postsession booster training resolved the degradation in most cases. We discuss these findings in relation to their clinical implications and directions for future research.