After a lesson, I used to give the students 2-5 problems to solve before I gave them the assignment. If they missed anything, I would send them back to fix the mistakes. The conversation went something like this...
Me: You missed three problems.
Them: Which ones?
Me: I'm not telling you.
I really like this idea of exit cards. It's a daily record. An informal assessment. A means for grouping students. A guide to instruction. Darn good stuff.