Generalization PhasesGeneralization probes were taken to determine if the participants were able to generalize use of two-symbol messages to novel play scenarios (i.e., Play Scenarios B). Two 15-min probes were taken for the first generalization phase, in which the instructor did not provide aided AAC models. If a participant did not produce at least 12 multi-symbol messages by the second probe, the child completed a second generalization condition in which the instructor provided aided AAC models. Generalization probes began within 1 week after completion of the intervention phase.