1) Good teachers want to teach.
Public schools are full of bureaucracy... there is so much needless stuff you need to do that teachers are willing to be paid less to work in a private school because all they have to do is teach.
The worse your school district is doing the more Bureaucracy you have to go through as they try different kinds of efforts usually without even bothering to consult the teachers.
The worse your school system is, the less time as a percentage your teacher spends teaching. So why work for a public school in a bad neighberhood? The answer... they make more money. Which isn't the best incentive for those who want to teach.
2) Rich kids learn in the summer. In studies where they test the achivement gap between the rich and the poor... the gap is actually LARGER at the start of the school year and closes by the end of the year... then is larger again at the beggining of the next school year.
Rich kids are more likely to be taken to muesuems, or taken to field trips or be enrolled in some kind of summer tutoring or even just pushed to read more books.
Switch it around, to where a poor kid is doing all that, and a rich kid isn't? The gap closes more.
