Honestly that's a good idea and i pretty much let my daughter do the same. Seems to be working, she gets the school work done and doesn't disrupt the class either, of course there are some bad days, but we just brush those away. No point to make her feel even worse over those one offs. Luckily nowadays most teachers acknowledge mental differences as well and actually allow kids some fidgeting toys or plushies or even listen to music when doing some independent exercise.