When an individual has a significant expressive communication deficit, he or she may engage in a variety of behaviors that might serve as substitutes. If any of these substitute behaviors produce social interaction (for example, in the form of attention or access to items), those behaviors will naturally be shaped into what could be viewed as a communicative repertoire for that individual. Unfortunately, these repertoires of substitute communicative responses may include challenging behavior such as screaming, destructive behavior, aggression, or even self-injurious behavior. When challenging behaviors occur repeatedly, systematic assessment based on direct observation is conducted to specify what types of social interactions are functioning as reinforcers for those behaviors. Then, for this population, intervention is often based on teaching the individual a more socially appropriate communicative response to replace the challenging behavior but produce the same reinforcing social interaction.