I absolutely hated school when I was there. That said, I dropped out in 7th grade (So much for the no child left behind program.) because of my anxiety and a few other things.
As much as I hated 6th grade I absolutely loved being a recess safety patrol. My 6th grade teacher hated my guts because my cousin was dating his daughter, I hated going to class each day but sometimes I'd go just because I knew I was going to be the safety patrol at recess that day. I absolutely loved being in charge of the younger student's classes (K-3rd.) while the teachers were out to lunch. It was one of the most rewarding things I've ever done. I loved it when I was patrolling the kindergarten class, the kids loved me because I was always doing weird crazy things with the blocks during indoor recess (Myself and the person assigned to patrol with me would take the blocks and build a tower all the way up to the ceiling, we got told off by teachers soooo many times for doing that.) And at outdoor recess the other patrol and I would play a game where the younger kids would chase us around and try to catch us, was good fun. I also loved the responsibility. If I could go back to 6th as much as I hated the actual class, I probably would just for the patrol part of it. I've thought about volunteering at the local elementary as a recess aid but the last thing I want is for them to find out I have an account here and have them think I'm some kind of pedo.
However if I could go to any grade any time, whenever I wanted to, I'd probably pick something like preschool, daycare, or kindergarten. I never actually went to daycare, only preschool and kindergarten, but I think it would be fun to be little again, and be able to wear diapers to class and not have to worry about it and be treated all little. I know there are places that have that kind of thing for adults but there aren't any near me that I know of.