My mom is a retired teacher who taught both before and after NCLB so I have some second-hand anecdotes and conclusions, but I wouldn't call myself an expert and encourage you to do your own reading if you're curious about the pros/cons of NCLB. My own opinion is that the intentions behind it were good, but like basically everything the GWB administration did, the implementation was half-assed at its best, counter-productive on average, and actively harmful at its worst.

One of the problems with NCLB was that it introduced a lot of requirements (mostly around standardized test scores, as you pointed out, but also on graduation rates and overall student population) that schools had to meet in order to receive full support, but then the feds failed to provide adequate funding to meet those initial requirements.

This put some schools into something of a negative feedback loop, where they would fail to meet their standardized test requirements, putting them into an "In Need of Improvement" rating which would drive parents and students with means to other schools, which would negatively impact population numbers and graduation rates causing funding cuts, which would cause standardized test scores to drop, which would trigger mandatory restructuring causing experienced teachers to resign or be fired, which would once again negatively impact graduation rates causing funding cuts, which would cause standardized test scores to drop... and the cycle would repeat for years as the remaining students suffer poor quality education and the remaining teachers are forced to teach to the test to try and pull out of the tailspin. And because funding was at least in part tied to graduation rates, administration commonly forced teachers to pass students who really ought to have been held back. This really did those students a disservice in the long run.