Even public school has more competition, more stay late. But from my observation, it really depends on the kid. I have two kids of my own. My older one is a freshman in a IB program. Over the summer, she challenged Algebra II, now she is in pre-calc class. She is in school tennis team, practices every day from 3 to 5-6, starts doing homework at 6 or 7, goes to sleep around 10, gets all A. My other kid is only 7th grade, IB, takes long time to finish his homework, has B+ ave grades.
Public school really provide more choices for different type of kids. The problem is from the parents who saw other kids are better than theirs, then they start to push , and push their own kids...