In the present study, the communicative spontaneity of 23 children with high support needs who used Augmentative and Alternative Communication (AAC) in a classroom setting was evaluated. In contrast to previous research, spontaneity was evaluated on a continuum rather than being treated as a binary variable. Spontaneity was found to be highly variable, but some students clearly lacked the range of spontaneity that would be associated with fully functional communication. Aided AAC systems were notably less spontaneous than signing or nonsymbolic communication. There was also evidence of systematic variation in spontaneity across pragmatic function, with instrumental functions being more spontaneous than commenting. The results of the present study highlight the need to consider spontaneity when assessing individuals who use AAC systems.