No, I wouldn't thank them. My life at school was hell. But I forgive them, after all, they were only kids.
About 10 years ago, I was at a pub having lunch. The manager came up to my table and said "Are you ____, is that you? I'm ____ and we went to school together. I want to apologize for all the teasing and bullying I did to you. I've felt guilty about it all my life."
I got tears in my eyes, and told him not to worry, we were only children, and I had forgiven him long ago. (Also, it helped that he was only a prankster, not one of the scary kids who used to beat me on a regular basis.) I thanked him for his kindness, though, and told him how good it felt to know there were people in the world like him, who cared so much about others' feelings.
tal