R., it is important to have him tested for dyslexia and any other possible learning disorder which may be hindering him. The law requires that the school disctrict not only provide the testing but also the treatment once a disability is diagnosed. The testing is done thru the County Educational School District. They can be found in the phone book.
Your son's school can and in fact should've given you this information. You can call the school's office and ask for more information. If they do not help you call the Educational School District Office directly.
My grandson, at age 3, already has an Individual Education Plan in which he is getting speech therapy as well as other testing and treatment options, because he is speech delayed. We learned of this option thru his pediatrician because she suspected he was developmentally delayed in learning speech. I think that with something like dyslexia the pediatrician wouldn't make that recommendation because he doesn't screen for dyslexia. But the school certainly should have.
Parents of children with disabilities have to advocate for them by arranging for assessment and treatment. It is too easy for them to get lost in the system just as it appears that your son has slipped between the cracks.
There are several good web sites that give information about this law and the IEP as well as about learning disabilities.
I wouldn't wait to see if his situation works itself out. We did that with my grandson and it didn't. He's starting out a year behind where we should've gotten him diagnosed. This has not only affected his ability to speak but also affected his behavior in a negative way. The longer you wait the longer your son experiences difficulty which makes it more difficult for him to catch up. And if he is not dyslexic you know better where to place your focus.