The truth is those school system are toxic, abusive torture to someone smart. There were plenty of smart kids I knew -- some smarter than me -- who got horrible grades going through one of these school. Many of them did not, in any real sense, succeed.
Imagine being placed in a room, today, and forced to listen to lectures on what you already know, and be given menial make-work tasks, like adding big numbers and copying letters, and doing that for hours each day. Some people are resilient enough to survive that. Others get pretty broken by it.