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.

Literacy skills are fundamental in modern society. A significant portion of information is conveyed through written language. With the widespread use of the internet, written communication has become even more influential in our daily lives. The ability to read and write supports cognitive development, enhances social interactions, improves comprehension, and contributes to academic achievement. Conversely, a lack of literacy skills can limit access to general knowledge and deprive individuals of these important benefits.

One group that stands to gain significantly from literacy skills is individuals with intellectual disabilities who use augmentative and alternative communication. For these individuals, reading and writing can lead to enhanced self-esteem and increased opportunities for inclusion in school, the workplace, and the broader community.

Research has shown that individuals with intellectual disabilities who use augmentative and alternative communication can learn to read and write. However, it is crucial that literacy instruction is tailored to their specific needs.

Inclusion Criteria:

• children diagnosed with intellectual disability, confirmed by multidisciplinary assessments carried out by the Child rehabilitations service or currently undergoing such an evaluation
• ages 4-8 (the last year in kindergarten)
• lack of functional speech and must use augmentative and alternative communication as the primary form of communication
• have a (designated) special education kindergarten teacher

Exclusion Criteria:

• having a severe visual or hearing impairment
• children who can decode syllables or words
• children with severe physical disabilities prevent the children from being able to answer with their fingers, unless they can respond with eye pointing or signs

Following the Findable, Accessible, Interoperable, Reusable Data Principles, the trial protocol, its registration, and models created to analyse the data during the project will be made available on platforms such as Open Science Framework and https://clinicaltrials.gov/. Project objectives and results will be communicated to the general public through newsletters, social media, mainstream media (regional newspaper), and presentations at showcase events. Lastly, we plan to launch a publicly accessible website of the project, describing the project, including its goals and the partners.

Study protocol: August 2025- August 2028 Statistical analysis Plan: August 2026- December 2027 Analytic Code: August 2026- December 2027