We found out that our son was intolerant to corn and milk after having NAET testing done by an awesome chiropractor that specializes in pediatrics, Dr. Don Galovich. If you're anywhere within driving distance (he's in Michigan), I highly recommend him (no, I am not being compensated in any way for recommending him). He was recommended by another fantastic (or so I've heard, since I don't have personal experience) chiropractor on the other side of the country, in Nevada- Dr. Shadia Koury.
If you've never heard of NAET testing, I suggest you do a bit of research on it. I can tell you- it isn't for everyone. Even I thought it was strange, and I'm a bit out there as far as alternative treatments and testing. But you know what? We kept an open mind, figuring if it didn't work then we'd go for further testing (blood tests).
And work it did. We went from having daily meltdowns, behavioral issues and him not being able to focus for more than 30 seconds at a time to having age appropriate meltdowns, behavioral issues and being able to sit and focus for a normal amount of 5.75year old boy time.
Now, I'm not saying that we removed corn/soy/milk from his diet and the clouds parted, the sun shone down and rabbits started pooping rainbows. He's still a 5.75 year old boy with a ton of energy and an "I know more than my parents because I'm almost 6" attitude that I would expect from a teenager rather than a kindergartner.
But the difference is like night and day, and I can tell when he's ingested something he shouldn't have.
You might be thinking "yeah, but how much of the difference is just that he's getting older/maturing?" To be honest, I'm sure that's part of it. However, he attended individualized play therapy for an hour a week for over a year with almost no progress. After a few days of removing the offending foods there was a noticeable difference, and after a few weeks he was like a completely different kid (in a good way!)
I don't know how it works, and to be honest I really don't care because it has changed our lives for the better.