So if he hasn't done his CPL, he must be fairly low hours still, perhaps around 80 or 90? In this case I can see 6 flying hours may not quite be enough to pass the MEP test outright, there is a lot more to handle with variable pitch props, retractable gear, all with their own set of limitations, it's easy to slip up and exceed one of these limitations which would be an automatic fail.
Having done many ME endorsements I can't see how you would ever need to spend 7 hours in the classroom.
I pity your students. I could sit in a classroom for 7 hours teaching about VP props and retractable gear, asymmetric power theory, performance comparisons between single engine, multi engine, and multi engine operating on one engine, and I'd only be scratching the surface.
The shouting on it's own is not good, but coupled with the apparent lack of groundschool it doesn't sound like a good recipe. It may be they've been including pre-flight briefs in the 7 hours of theory on their paperwork, which isn't really how the course is intended to be. There is a written paper, and it's good to know you've been prepared for it. Although you say the 7 hours theory isn't on the horizon, their notes may show it as being completed.
You need to talk to the CFI at the school and get a good idea of where you son is in his progression, and what realistically needs to be done. If it's just a couple more hours it's probably worth persevering, as if you go to a new school the first thing they will do is a check flight which is a waste of money really. If they're really saying he's nowhere near ready it might be time to cut your losses and find a different school.