Back when No Child Left Behind was passed, our nation decided that all school children are identical and any performance difference had to be the fault of the teacher.
We do in fact know many factors that affect student performance. For example when a child changes schools, it's equivalent to a loss of several months of schooling. Children from dysfunctional families tend to have problems in school. Children whose parents don't read regress over summer vacation.
But since it's politically convenient to assume all children are exactly the same, we no longer discuss these issues. It's far easier to dump on the teachers taking on the toughest cases.
We do in fact know many factors that affect student performance. For example when a child changes schools, it's equivalent to a loss of several months of schooling. Children from dysfunctional families tend to have problems in school. Children whose parents don't read regress over summer vacation.
But since it's politically convenient to assume all children are exactly the same, we no longer discuss these issues. It's far easier to dump on the teachers taking on the toughest cases.