A common way of teaching in a multi-grade classroom is to have students check their own work. The biggest reason for this is that it can help the teacher manage the amount of grading and give the student quick feedback on how they did. There are several problems with this though. First you have to still spot check to make sure that they are being honest. Second is that when most students get the answer wrong they simply mark it wrong and don't think about why. A solution to this is to have an electronic grader which tells the student whether they got the answer right or wrong but doesn't tell them what the right answer is until they get it right.
I'm currently trying an experiment with my 5th grade students to see how well this works. I've input as many questions as possible from their textbook into Moodle, an online learning management system. They have used it twice now and ask for help when they can't figure out what the answer is. Which is exactly what I'm wanting. They try to figure it out and if they can't they ask for extra help.
Currently the biggest problem with this is that more complicated problems are harder to enter into the system.
I'll post more about the results later.