Effectiveness of an Early Reading Intervention for Young Children With Intellectual Disabilities Who Need or Use Augmentative and Alternative Communication

The goal of this 2x2 factorial randomized controlled trial is to evaluate the effectiveness of two literacy interventions delivered at different time points, in kindergarten and in first grade, on the development of literacy skills in children with intellectual disabilities who require augmentative and alternative communication. The main questions it aims to answer are: * Does early intervention in kindergarten lead to greater improvements in phonological and phonemic awareness, vocabulary, and articulation compared to training as usual? * Does a follow-up intervention in first grade enhance decoding skills and sight word recognition beyond the gains achieved through the kindergarten intervention alone? * Does phonological awareness at the end of kindergarten mediate the relationship between early intervention and later outcomes in vocabulary, articulation, and decoding? * Do children who receive both interventions perform better than those who receive only one or none (training as usual), suggesting a cumulative or higher-dose effect? Researchers will compare four arms formed through a 2x2 factorial design after randomization to see if whether timing, combination, and sequencing of interventions produce differential effects on literacy outcomes. Participants will: * In kindergarten receive either an early literacy intervention or training as usual. * In first grade receive either a follow-up literacy intervention or training as usual, depending on group allocation. * Be assessed at key time points in both years, measuring phonological awareness, phonemic awareness, vocabulary, and articulation in kindergarten, and expanding to include decoding and sight word recognition in first grade.