Maintenance probes were conducted 2, 4, and 8 weeks following completion of the generalization phase. The procedures for the maintenance phase were identical to those used during the interven- tion phase; that is, the same play scenarios were used and the instructor provided aided AAC models. Aided AAC models were provided during this phase, because failing to do so would essentially have been a return to baseline condi- tions, thus introducing an ABA component into the design, which is not part of multiple baseline designs. Furthermore, the participants’ abilities to produce symbol combinations without aided AAC models were examined in the generalization phase. If any participant had used fewer than 12 multi-symbol messages, additional ‘‘booster’’ sessions would have been implemented.