Aspects of the classroom environment relevant to the communicative spontaneity of 23 children with high support needs who used AAC were examined in this study. Specifically, antecedents associated with different modes of communication and the effectiveness of requesting and rejection were examined. Most communication was identified as occurring in natural routines. Aided AAC was predominantly associated with prompts, such as questions and, in particular, system presentation. In relation to the pragmatic functions of requesting and rejecting, the probability of communication being successful decreased with increasing spontaneity. Several possible implications of these findings for intervention are discussed.