D.K.
Have you spent a day observing the classroom? Some children need a teacher to have an individual connection with them to really listen - some mostly new) teachers just give blanket instructions to all (without having established a personal or individual connection first). Perhaps he is bored/not challenged in the classroom. Perhaps the 'work' is beyond where he is and he is not asking for/receiving help. I think you need to know what the issues are.
I personally do not believe in 'rewards' or ' consequences' for teaching children. Learning should be self motivated and I do not believe this is what rewards teach. I would be really upset if a teacher tried rewarding my son with stickers or a chart. But if this is the system you use at home, maybe it will work for you.