Metadate is a ritalin derivative, so is concerta. There are several medications that are not stimulant. I would also reevaluate the idea that he is alergic to ritalin, not that it could not happen, but in years of working with ADHD childnen and their parents, this is the first time that I have heard that.
I would suggest that you find a pratitioner who is very good at prescribing these medications (look for a board certified child psychiatrist) and find what works for him. If you are not also accessing therapies, then start now because medication alone is not the answer. Also, there is little data that the natural-diet based treamets work, and the miricle success stories you will hear are anecdotal and will most likely not apply to your son. Be very aware that anyone outside of the standard medical-theaputic community who is trying to sell you something may mean well, but is playing on your desperation.
As for holding your son back in school, please be very vigalant here. If he is behind in his academics, one more year of what did not already work is not going to help him any more, he needs something new. It will hurt him in the long run to be held back. He will not be elegible for specific intervention for reading, writing, and math until he is behind his grade level peers, and by holding him back you only delay appropriate, targeted, and effective intervention by one year. The school will refuse to look at his age. This is a MAJOR concern because the window for reading development closes at the end of his third grade year or so, and you want him to have one more year of targeted, effective reading intervention if that is what he needs before that opportunity for very effective remediation is gone.
Also, statistically, as an older teen he is far more likely to drop out of school, be involved in drugs, and have contact with the juviline justice system if he is older than his peers in high school. This is well documented, so please check out what happens later in life before you hold him back now.
Holding him back is easier for the school, but it is almost always the WRONG thing for kids.
Read anything by Dr. Mel Lavine or Dr. Russel Barkely. They have terrific strategies for helping ADHD kids. Check out www.wrightslaw.com and get him a speical education evaluation as soon as you can.
This is not just a matter of "maturity" and the school may be upset with you for not keeping him on meds, but you should point out that this is the very reason that they need to do a full evaluation, so request this in writing. You should get one too from a neruo-psychologist or developmental pediatrician, because you should NEVER know less than the school about your son and YOU should own the evaluation that holds his diagnosis.
Good luck,
M.