At some point a few decades back, "reformers" who wanted to improve American education got into the habit of overstating the problems with American public education. They won a lot of political success, and have done enough things that now people who don't like the reformers also like to overstate the problems with American public education. So you have a narrative dominated by tales of failing union-ravaged schools and declining drill-and-kill reformer-ravaged skills even though the evidence suggests that, as Kevin Drum argues, the school system is actually steadily improving.
An interesting thing about the politics of this is that polls continually show that Americans rate the schools in their own communities quite highly, even while having a dark view of the school system as a whole. I take this as a sign that on some level people actually know the good news about American education. There are still lots of kids—especially poor kids whose parents have weak education backgrounds or kids experiencing a lot of disruption in their home life—who aren't doing as well enough, but the trends are pretty clearly on the upswing.