Roldrik-
What would be interesting to me is to see what the average test score is for the PARENTS of our nation's children.  I'd bet we'd be close to last in the industrialized world.  Why?  All kinds of reasons: alternative "facts," fake news, and a love-fest with a trillion dollar entertainment industry that makes us happy at the expense of a reasonable grasp on reality.  How many kids play video games when they have free time?  How many did that 50 years ago?  How many books does the average kid read now?  How about 50 years ago?  
I'm not saying we should go back to the 1960's, but rather the past times of the typical child have changed mightily in the last several decades.  As such the priorities of today's kids are much different than of those then.  Teachers face an incredibly daunting task in trying to educate children who have little interest in being educated - their idols are literally superheroes, not firemen, doctors, etc. who live in the real world.