I don't have experience with public school in the US but my SIL teachers elementry school in midwest for many years. Her students sit on stability balls in class. I did a quick google search finding many articles on the topic, for example: http://life.gaiam.com/article/how-sitting-ball-helps-kids-focus-and-do-better-school

It can be especially useful for children with ADHD... but obviously won't solve issues with the material being covered ;-)