D.O.
Although my son is now 24, when he was in 2nd grade (which really not sure if that around the same age or not) he was still sucking his thumb. We did just like everyone else has and that was tried it all. The strange thing is his older sister sucked her thumb up until she turned 5 and I looked at her and said aren't you getting a bit old for that since now you're a big girl and she stopped from that point on in public, and soon broke herself of it at night. Just shows you the difference in kids.
Anyway back on subject. We did use a device that the dentist placed in the mouth. First it was all rounded and nice and well all I can tell you is my son worked around that little puppy and soon broke it. So our Dentist took the broken one and removed the rounded piece at the bottom and left the three little points, nothing that would really harm but that would discourage. All I can say is within less than 1 month he was done sucking his thumb, and there was no more broken expensive appliance to worry about. It was removed and that was the end of that.
So yes I would highly recommend it. I think it help him with his self confidence since he really did want to stop, but just like any addiction sometimes we need a little help and I believe children in many cases are just the same. I wish you the best in what ever you choose to do.
As for a recommendation the dentist we used was Dr. Lee I believe he is out on 75th Ave & Bell Rd. I know because my oldest daughter still uses him. He was wonderful with children and obviously adults. If you can't locate him and want his number let me know and I will get it for you.