Culture Shock
For many it is a much bigger change than they where prepared for to have your life dictated to you, you appear to have no power to decide you future, and have people jump all over you for making a mistake.
For most kids this is the first time that failure is not an option, taking your time is not okay, close enough does not cut it, the best is not expected but demanded, and failure to achieve these is met with not only getting yelled at but pain and fatigue. This can be hard on allot of kids of modern society.