Just read this opinion piece in the NY Times. Here's my favorite quote from the whole thing:
Schools control only a small part of what goes into test scores.
Cognitive ability, personality and motivation come mostly from home. What happens in the classroom can have some effect, but smart and motivated children will tend to learn to read and do math even with poor instruction, while not-so-smart or unmotivated children will often have trouble with those subjects despite excellent instruction.
Every single one of us in education know this! Why don't the politicians?