U.S. schools from kindergarten to high school have avoided a spike in COVID-19 cases, early data show, but medical experts say the real test is coming as students in large densely-populated cities such as New York and Miami return to classrooms. The CDC this week said more than 270,000 COVID-19 cases had been reported in children aged 5-17 since March. Cases in school-age children ticked slightly higher in mid-September as more schools reopened, but remains well below the peak set in mid-July.