This study examined the effects of an intervention that integrated peer-mediated instruction (PMI) with augmentative and alternative communication (AAC) using speech-generating devices (SGDs). Nine trained peer tutors without disabilities taught science concepts and modeled use of SGDs following a script to three elementary school students with significant cognitive disabilities in Taiwan. Using a multiple baseline across participants design, results showed the PMI with AAC intervention was effective in improving participants' targeted science knowledge. In addition, participants increased their communicative interactions with peers and increased the use of different communication modes during the science experiment activities with the implementation of PMI with AAC, when compared to the communication responses during the general teaching strategy.