Andreas Schleicher, the head of education and skills at the O.E.C.D., told The Financial Times, “Thirty percent of Americans read at a level that you would expect from a 10-year-old child.”

Schleicher attributes part of this decline to the increasing consumption of short-form digital content, such as social media posts and videos, which may reduce individuals’ capacity for deep reading and critical analysis.

Scores for children at the top of the distribution are not falling. It’s the scores of children toward the bottom that are collapsing. The achievement gap between the top and bottom scorers is bigger in America than in any other nation with similar data.