It is unfortunate that he did not get help earlier. It is critical that all of his needs be addressed now. Have you been to the public school yet? He is eligible for a program called Child Find.
Your description suggests that in addition to his learning disability (current school term for dyslexia) he might have a receptive/expressive language disability.
“Adversely affecting educational performance” is a phrase from the IDEA (Individuals with Disabilities Education Act). The interpretation of this phrase has been debated for many years.
Communication devices can often be large, bulky, and single out AAC (augmentative and alternative communication) users as “different” from their peers.