Augmentative and alternative communication (AAC) technologies can help bridge the gap between severe speech impairment with poor intelligibility and true language potential. By using AAC, preliterate children with intact receptive language skills can rapidly learn to produce novel, grammatically correct graphic symbol sentences. Two case studies from a larger five-year investigation designed to teach preliterate preschool children to produce sentences using a graphic symbol-based AAC application are presented. The first case is a four-year-old, presenting with intact receptive language skills and speech impairment, resulting in 26% intelligibility with context and 6% without context on the Index of Augmented Speech Comprehensibility in Children, I-ASCC. The second case is a five-year-old with Down syndrome and speech intelligibility of 19% with context and 13% without context on the I-ASCC.  The AAC Generative Language Intervention (AAC-GLI), supporting production of sentences using a graphic symbol-based AAC application is presented, along with pre- and postintervention language analysis of aided utterances. Participants received a total of 21 to 28 play-based aided language intervention sessions over three to four months. Both boys demonstrated significant progress and growth in their semantic and grammatical development using graphic symbols, as evidenced through the use of accurate word order, relevant symbol use, utterance length, and range of vocabulary across word classes.