It's tough to flunk entirely out of the school I went to because they are big on their safety net. If a student failed his CDL tests, they'd work with him until he passed. They let people practice with the trucks before and after class (range and pretrips only). They never let someone flunk outright without doing something. People did fail, however.
We had students who had a heck of a time getting it together on the range. They couldn't back for beans no matter what they did. They would get frustrated and try to quit, but they'd be back in two days studying for the Class-B instead of the Class-A. The rest of us practiced over and over and over until we finally made it work.
We had a lady who wanted to go OTR, but neglected to mention she was a single mom to an 8-month old and a 4 year old. She fully planned on living and raising/homeschooling her kids in the truck. She quit when she learned there's no way that was going to fly.
We had another student who started off fine, but then kept showing up later and later. Then he didn't show up at all. The reason: He broke up with his girlfriend and she was his only transportation to school. He lived too far away for the bus. I guess no one from class offered him a ride.
Another person (whose last day was my first) was picked up for a DUI. The school told him continuing made no sense since he wouldn't find any legit work in trucking, anyway. When he was there, he also got kicked off the range a couple of times for not having his license and medical card on him. Instructors asked for them often. You absolutely could not be in the truck without your papers.
I didn't run into any know-it-alls when I was there. I made a few great friends and I have a lot of respect for my instructors. It was a good program. I'm also grateful that Career Services didn't just toss a bunch of Werner/CRE/Swift/Knight fliers at people and call it a day. They made an effort to match people to good opportunities and they warned students away from companies that treat drivers badly. They also made sure to teach people what to expect and how to live on the road. They didn't tell people they were going to make 100K their first year. I'm glad I picked that school.