7 year old angel at home, bad at school... Help?

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I really need some good advice here, my 7year old son is one of the best kids you could ask for. He almost always listens at home, is very respectful and helpful, an all around sweet boy. But when he goes to school it's like another side of him, he doesn't listen, doesn't stay on task, and does things he knows are wrong, like yelling in the halls. We have taken things away and made him sit in his room, we also spank him. But none of this is getting through to him. We don't know what else to do, it's hard to discipline him for behaving bad when we have never seen that side of him. If anyone has advice, please do give it.
I also want to add that he get's attention at home. My husband and I are always having family time, we have family dinners and play fun family games.