Your post could have been written by my brother. Your DS sounds just like my nephew who, by the way, is off the bus for a week due to bad behavior. This however, is the first of the really bad behavior we have seen for about 2 months so what his parents are doing, does seem to work.
1. He was evaluated by a pediatric therapist and now sees him once a week, soon to be cut down to twice a month.
2. Everything he owned, tv, toys, games, anything except books, was removed from his sight and, when needed, was used only in the supervision of an adult. He does have 3 other brothers and was not permitted to go into the rec. room to play.
3. He earned "Behavior Buck" for good behavior. At first, this took a lot of time because he had to be occupied by an adult. The adult dictated what was going to be played like a game (no video games, the "old fashion" board games). When he showed good behavior by saying something nice or being a graceful loser, he earned "Behavior Bucks".
4. After earning the "bucks", they can't be taken away. He can trade in the "bucks" for tv time, a toy returned, special privileges like spending the night at Grammy's.
5. His teacher is wonderful and charts his behavior at school every hour. For every smiley he has, he gets a "buck". The bus driver sends a smile or frown card home to indicate the bus behavior.
6. When out of the house, with his parents or family member, he carries a small clip board. For every 20-30 minutes he's doing what he is suppose to be doing, he gets a smile on the clipboard circled. He earns a "buck" for each one of those.
7. The therapist said to focus on only good behavior, remove him from the situation if bad behavior occurs and take him immediately home to his room.
8. It took a lot of time but it is working. When he didn't have any toys or tv, he needed to be supervised or played with by an adult. This was good because he got a lot of positive attention from people who loved him. We are a close family and I don't have children yet, so I played or rode bikes with him a lot.
My take on the whole thing was he needed attention and felt "lost in a big family but I don't really know what caused it.
He's a different kid and we are so blessed by the help we received. Good luck to you, I hope you find an answer.