Programs/supports for special needs vary by state.--Early intervention (birth to five years) and then school age supports all vary by state. Diagnosis should be by qualified professionals--a diagnosis is not the same as an educational classification, which is what the IEP uses (in NY state). However, the diagnosis may indeed be what helps to determine the educational classification.
Often, some diagnosis can't be made until later (i.e. second grade/ 7yrs old) as the assessment tools are standardized for those ages for certain diagnosis.
Paige--it's not easy to finally hear that diagnosis--but your little man is the same guy you went to assessment with. He's your boy--you will take it step by step. I know you have it in you to follow your instincts. (((HUGS)))