M.B.
Absolutely this approach has been shown to work. Take a look at Dr. M. Ann Block's website: www.blockcenter.com
She's located in the Hurst/Bedford area so is a bit of a drive for you but she's one of the topic experts in this area (nationally and internationally), so we are very, very lucky to have her in our area. She has written a book that is a self-help guide for parents to follow just this approach. I met with her and she absolutely amazed at how few parents are willing to take this approach. She herself got into medicine when her daughter was made very ill by Rx drugs - she knew there had to be a better way.
Also, there is research that shows the impact of the ADD/ADHD drugs on physical growth and most recently, they've realized the brain growth is slowed. Thus, these poor kids are on track to have issues for a very long time.
There is a video on Dr. Block's website that shows a boy's reaction when he's given something he's allergic to. You can watch as his behavior goes from calm (and handwriting legible) to being totally out of control.
My two sons are on a GF/CF diet and we have removed all articial colorings, preservative, etc. and it has made a huge difference with behavior issues. Older one had many Asperger's symptoms and younger one had the ADD/ADHD. Also, I follow this diet and have found the recommended supplements to be extremely helpful. As these problems are often genetic.
You can test for the gluten and dairy issues using enterolab: www.enterolab.com
Good Luck!