Everyone is going to name their pet bugaboo, but if you look at the full charts, the scores were pretty stable in the 70s, 80s, and 90s, and are regressing back down to what they were historically. The real question is why they went up temporarily until 2012.
I wonder if having the Soviet Union as an ever looming adversary could have something to do with it, and after their fall everyone just got complacent.
Few people know this, but it turns out a major bipartisan education reform bill was passed in the early 2000’s.
Constituencies of both parties found reasons to hate it, so its foundational accountability requirements were watered down by succeeding administrations.
I’m perfectly willing to be convinced NCLB had nothing to do with the evolution of test scores over the last 25 years, but the circumstantial evidence is not easy to dismiss.