You've gotten a ton of good advice. I just wanted to chime in and say it's hard at first, but it does get easier as time goes by. And you may be very surprised at the effect foods have on your child. I know when my DD gets hold of allergens or artificial stuff she is a completely different, CRAZY child with absolutely NO impulse control at all whatsoever, and I'm not even kidding or exaggerating. I'm convinced that if I hadn't been feeding her the way I do for so long (we've been casein-free pretty much all her life b/c she reacted to it when I consumed it and then nursed her, and I've always avoided artificial colors/sweeteners/preservatives with her), I'd have had her evaluated for ADD or ADHD or other behavioral issues by now.
If you like email support lists, there's a really good one at Yahoo called
foodlab full of really knowledgeable people who have done food elimination diets for a long time and have tons of information.
I've found that I can put a lot of our pasta dishes over rice instead without too much change in flavor. The texture is different, of course, but it helps that we love rice.
I haven't seen this mentioned yet, but unless oats are certified gluten-free, they are VERY likely to be cross-contaminated with gluten due to where they are grown.
Gluten also hides in soy sauce - that's the one that always gets me if I'm not really thinking about it.
Oh, and most beer contains gluten but that's not an issue for your son!
