This study compared the communication of two older male adolescents (aged 17 and 19 years) with each other (peer interaction) and with a teacher (non-peer interaction) in three different types of activity (casual conversation, providing/listening to a recount and collaborative problem-solving). Conversation analysis, selected analyses from the perspective of systemic functional linguistics and social psychology (communication accommodation theory) were applied in data analysis. Peer interaction showed fewer questions, fewer challenging moves and the absence of divergent accommodation strategies. In the non-peer interaction, the teacher's higher number of turns, questions and interruptions appeared to influence the opportunity for adolescent contribution to the interactions. Some aspects of language use by each adolescent--mean turn length, use of one-word utterances and sarcasm--were consistent across communication partner and activity. The methodology is suggested to provide a suitable procedure for use in similar research with older adolescents who have traumatic brain injury. (Contains 1 table.)