No Child Left Behind increases the dropout rate
The largest study done to date clearly indicates that the No Child Left Behind policy significantly increases the rate of high school dropouts. Frankly, this is no surprise to me, as the misguidedness of NCLB's test-and-accountability approach has been very clear to me from the beginning, because it incentivizes teachers and schools to teach test-taking rather than general education and flexible thinking.
And the study concurs with that thinking, but also brings up another, darker effect: because schools are scored by the test results of their students, school administrators have a strong incentive to "help" low-performing students drop out. When poor performers drop out, the school's scores go up. It's likely not that the administrators kick the kids out. Low performing students are the ones most likely to want to leave anyway. But now the schools have no incentive to fight to keep those kids in class.
It's always been easier to let the struggling, drop-out-minded kids slip away. But now it's actively better for the school if they do, because the school's performance rating will improve. And the study shows that this is exactly what is happening. The actual drop-out rate of urban Texas highschools is 33%, way up from before NCLB, and the more strictly punitive the NCLB implementation, the more students dropped out!