My son enters kindergarten next school year.  He's had the same teacher and many of the same classmates in his three years of special ed preschooling.  His social/behavioral differences are not autistic, not compulsive, not intentionally disruptive.  He can grab an idea and run with it instantly.  We were watching Caillou and they were cutting out paper snowflakes and he wanted to do that - right now!  His intensity and focus are great assets - so long as he is focussed on the same as the rest of the class.

I sometimes wonder if it's possible to have independent study for elementary school students.