dd1 is gf/cf.
she had the opposite result - very high gluten peptides, inconclusive for casein.
we cut both out of her diet (did casein first, and did see a difference) as she was a total gluten/casein junkie.
she lived on weetabix, yoghurt, pasta with cheese, cous cous - you name it, if it had gluten or casein in, she loved it.
it has been life changing for her. she was verbal beforehand, but minimally so. very echolalic, and no real interaction, beyond singing together or reciting stories together.
a couple of weeks in, and she was tlking to US, rather than just talking, iyswim? she had a normal pain reactionn (before she didn't notice), and was a LOT less dreamy and other-worldly.
what it did for her, most of all, was ot give her the headspace needed for her to be able to learn. she really was fogged up before.
wrt telling school: a tricky one. depending on how much your ds reacts, there are a whole lot of potential issues with school. eg PVA glue is flour based, play dough/plasticne is a no-go, a lot of paints have flour products in. even the glue used on stickers (dd1 used to continually stick them on her hands and peel them off, to get the reaction). skin transfer used ot be the biggest problem (I mention this because you might well cut down on gluten/casein, but not necessarily see a difference - and it could be that your ds is getting his "fix" at school...)
dd1 has been gf/cf for nearly 4 years now - it is tricky to eliminate it all at first, but once you get used ot reading labels, and not venturing into 90% of the supermarket, it becomes a way of life.