Learning declines have been substantial and pervasive.
Consider one example from the National Assessment of Educational Progress, or NAEP: In 2013, 74% of American eighth graders scored at the basic or above level in math, the highest figure since the test started in 1990. In the most recent round that number fell to 61%, hitting levels last seen in 1996. Scores have fallen in other grades and subjects, too.
Despite a small handful of relative bright spots, these declines have been remarkably widespread. Eighth grade math scores fell in almost every single state during this period; no states saw increases. Although schools that were closed longer during the pandemic tended to experience bigger declines, even those that quickly reopened have been hit hard by learning loss.