The episode, earlier this year, was one of numerous cognitive mix-ups that plagued Will, 15, after he contracted the coronavirus in October, along with issues like fatigue and severe leg pain.

As young people across the country prepare to return to school, many are struggling to recover from lingering post-Covid neurological, physical or psychiatric symptoms. Often called “long Covid,” the symptoms and their duration vary, as does the severity.

Studies estimate long Covid may affect between 10 percent and 30 percent of adults infected with the coronavirus. Estimates from the handful of studies of children so far range widely. At an April congressional hearing, Dr. Francis Collins, director of the National Institutes of Health, cited one study suggesting that between 11 percent and 15 percent of infected youths might “end up with this long-term consequence, which can be pretty devastating in terms of things like school performance.”

The challenges facing young patients come as pediatric Covid-19 cases rise sharply, driven by the highly contagious Delta variant and the fact that well under half of 12-to-17-year-olds are fully vaccinated and children under 12 are still ineligible for vaccines.