I usually failed at least 1-2 kids in every class......but if I did I had to have solid documentation as to why they failed. Most of the time it was because they didn't come to class.....I had a kid who scored less than 30% on every test I gave, missed 2 of the 5 tests completely, had 25% attendance for the semester, did none of the required homework and he challenged why I failed him with the dean of my department. I had all the docs so the dean backed me up, but the student couldn't believe I would fail him!
I was appalled at the poor scores on tests, considering they were multiple choice and often the "wrong" answers were just silly.....yet they still only got in the low 60%.....even my better, more experienced students. Remember I'm teaching automotive courses - steering and suspension could get pretty technical so I could understand some of why the scores weren't great, but mostly it was because no one did any of the reading or homework (all done online) and no one ever asked a question in class about something they didn't understand. I also taught a class on brakes (not breaks, dammit!) and 2 different Intro courses. The most important one was the Intro to Shop Practices, where I taught them how to use the different shop equipment, lifts, tire machines, balancers etc.
I also had to do a section on hand tools - where I would hold up a tool and explain what it was and what it was used for - something I thought any kid that wanted to work on his car would know but they didn't. Example - this is a pair of pliers - it is not a hammer, this is a hammer! We provided all the tools so not having any wasn't a valid excuse.
I remember one class where I was teaching how to use a torque wrench - it was a school requirement that anytime a wheel was removed the lugs must be torqued - with a torque wrench. Period. No exceptions. I decided it might be wise to explain why lug nuts and bolts had a tapered side and a flat side and which went where before we went into the shop that day. That very day a student brought his car into the shop to balance the wheels because they were shaking - and you guessed it, ALL of the lug nuts were on backwards.
I had another student in Steering and suspension - which was an advanced course requiring the all of the Intro courses before you could take it - who I sent with a tire and wheel over to the dunk tank to try and find the leak - I handed him an air chuck and told him to put 40 psi in the tire and dunk it. 5 min later he came back holding the air chuck and said he didn't know how to use it!?!?! I was OK with that as at least he didn't just try to wing it and I got to have a real teaching moment with him. Same kid put his car up on the alignment rack and while entering the info into the computer got stopped because the computer asked if his car was 2 or 4 wheel drive, and not only did he not know, he didn't know how to tell. Mind you, this is a 2nd or 3rd year advanced course.
My point is these kids - especially from the more affluent area my school was in - don't have the basic intrinsic knowledge and experience that many or all of us boomers grew up with. They don't have dads that had to fix their car on Sat so they can get to work on Monday - their dads just take the car to the dealer or shop if it breaks. Their dads don't have a shop full of tools, not even hand tools - they might have a screwdriver or claw hammer but not much else. They just call "the guy" when they need something done in the house.
Anyone who goes into the trades now is set for a great career, as fewer and fewer people know how to do anything that involves real work.