Aaarggghh!!!  Do you deal with this?  Sometimes a student will skip a line or measure, and when I ask him to go back and play it, he tells me he already played it.  He INSISTS he played it, even though he most definitely did NOT!  It is one of my biggest pet peeves, and it’s hard not to act like a little child and stick out my tongue at him!

What do you do when students do this?