We'd originally contributed some board books (more expensive than the usual paperback rewards) for Joy to take part in the system. But then with Joy not in the classroom much at all, and having the reward so far removed from the good behavior, on top of the rough way she treats books... she ended up getting more immediate small rewards instead, and just not participating in the classroom's system for the first weeks.
Until I was volunteering in the classroom one Monday. One dear little girl went out of her way to tell me that Joy was doing well (bless her heart!) But a young fellow at the same table wanted to make sure that the record was set straight -- or maybe he just liked "telling"? Anyway, he swiftly pointed out that maybe it wasn't so great after all, because Joy never got to go book-shopping.
So I took this perspective to Joy's team -- that, even if the reward system is not perfectly set up to be meaningful to Joy, the other kids are noticing and her participation (or lack thereof) has meaning to her classmates. They immediately agreed to make a change. Now Joy gets stars like the other kids, no matter what level of meaning they may or may not have for her. And if she's not in the room much that day, her aides make a point of coming to the teacher and announcing audibly that Joy should get stars for thus-and-such she's done OUT of the room.
The first full star-chart that came home with a board book brought tears to my eyes. Her teacher had signed it with the message, "I'm so proud of you!"