I like to have them storyboard their projects on paper first with a few brief drawings and comments about how it is going to work before they start to code. Then if their project deviates too far from that, I can ask some questions. Another thing if I suspect them cheating is that I look at their code and find anything that looks like it might not be their work and then ask them how they were able to achieve a certain effect or event. If they can’t explain it, they are usually pretty quick to admit it isn’t their code and then I offer to help them create their own project.
Mike