I’m not sure it’s entirely beneficial to go gluten-free across the board. Moderation is the key, I think. Have you tried spelt instead – it is an ancient form of wheat which does contain gluten, but my DS1 tolerates it but not so much regular wheat. I just always did separate dough for him, now he's in kindy two days a week I don't mind him having the wheat on breadbaking day. We try to keep him wheat free other times.
We were not built to consume vast amounts of wheat and corn, etc. – so it stands to reason it is becoming more of a problem, as food companies are pushing it more and more. We eat bread, pasta, more bread, pizza, more bread,…. We should be having more of a variety of grains, and preferably wholegrains and less refined ones.
As a side note, a very experienced and knowledgeable (and I think quite perceptive) anthroposophist commented recently to me that she believed the quality of wheat is different the world over, and here in Australia (and I’m thinking also in the US, not sure) it is harsher. She gave me an example of someone she knew who couldn’t eat wheat here but went to Europe and was easily able to tolerate it. Then came back here and was sick again if she ate the local wheat. She said she thought there was something in the soil that made it harsher.
Anyway, it’s certainly worth entering a dialogue about this with the school - The cost is an issue – with spelt and with gluten-free, I imagine too? Some playgroups will use spelt. Maybe they can do the odd/or planned spelt or gluten-free days? One of the issues with gf is that it’s high GI isn’t it? Wholewheat with grains is not…but hardly anyone does this I imagine anyway.