I'm debating this one. I feel weird about sending the stuff back, so if it's a scholastic offer I know my kids would enjoy, I go ahead and do it, and then just call and say I don't want any more. This is one my boys would surely enjoy, so I'll probably do it.
To answer the OP's question, scholastic almost always credits super fast. Never had a problem with not getting a credit. Their products are nice too, so if you have kids, it's an inexpensive way to get them a treat.