I think the star chart (or something similar) can work if the stars are linked to something specific. DS is pulled out for writing and the teacher gives him fake money and at certain times he can buy a reward from her. I think the fake money is tied to him actually producing writing during their sessions, not something really abstract like were you good today, or not good. I have also used bribes like this when I tutored reading, to get the kids to do their reading assignments at home. If they brought back their reading log with their parents initial, they could play "bingo" and once they won bingo, they got to pick a prize. It motivated some of the kids, not others. The star chart could get complicated if the teacher forgets about it sometimes or your DS disagrees about whether he should get a star or not. In any event, it sounds like you are making some good progress and have people who are concerned and want to help, which is the most important thing.
