I'd tell them that it would be a bad idea for me to write a letter as it would not be a positive one and would certainly hinder their attempts to pursue graduate study. I would probably discourage them from applying altogether.
It helped me to understand where they needed additional support and to get a good sense of how they'd respond to specific questions. When it was time to pitch questions with my boss for the exam, I would offer a bunch of fastballs, but no curveballs.
The room is a square shape, and the computers run along the wall, facing away from the projector screen. When I teach, I sit literally next to a student, and therefore can't "hide" my notes in my PP if I'm using one. I typically will have the software on the projection screen, and stand beside it with a laser pointer showing the various tools, etc. It's tough getting everyone to pay attention..