It's called government mandates along with teachers that are basically challenged. Mandated testing leads to teaching the test to the exclusion of all else. "No child left behind" was a huge incentive to cheat and cook the books. Any time government gets involved in anything it gets destroyed with constant manipulation.
If government was interested in teaching our children they wouldn't be so afraid of Charter Schools. It's not about teaching. It's about control. It's about tax money. It's about unions.

Want to get your numbers up just graduate everyone. It's more about social promotion than anything.