The no child left behind act was enacted in 2001. If you check the article, it has a nice little chart, showing a decline that starts in 2015. Prior to 2013, the results show a clear trend of improvement (in regards to the percentage of students achieving a minimum level of proficiency).
How would you explain that temporal gap? If the No Child Left Behind Act is the problem, why was the trend positive for the first 12-14 years of the time it's been in force?