Measuring two different things. Your number: can read the words, mostly understand the words they read.

6th graders are generally literate. However, they're not necessarily picking up on nuance, or subtleties. And they will often not take into account how the sentence they just read fits into the overall context of the piece, and they likely won't question the narrator, assuming they're reliable.

You can imagine how half of adults being that bad at these things has colored political discourse.