I posted questions a few months ago about doing a casein-free diet for DS (diagnosed with ASD in Feb). I figured I'd post my experience in case it helps someone else.
So, I tried it. And though I didn't see any radical improvements like so many people have mentioned, I was so excited when 3 weeks into it I started to see some improvements. Mostly less anxiety during school drop-off and social events with friends. At the four week mark, I decided to do a milk challenge and no reactions. So I gave him more the next day and even more the day after. By the fifth day, we were almost back to a normal diet and still no issues. In fact I was seeing further improvements - better behavior at school, asking to go to birthday parties, etc
So, we are off the casein-free diet. My guess is it is the OT and ST that are working - much quicker and effectively than I would have expected (he's only been in therapy 2 and half months). I am very glad I did the challenge and we didn't continue the casein-free diet when it wasn't necessary.
My advice is to definitely do a challenge when trying an elimination diet.
Re: Casein-free diet
It's definitely a good idea to see a dietician. We had great success getting my dd to no longer be underweight through smoothies. We blend fresh or frozen fruit and veggie, hemp, and flaxseed together and stir it into kefir.