New York City’s schools are showing encouraging signs that the resumption of in-person classes has resulted in a surprisingly small number of positive coronavirus cases. Out of 10,676 tests in one week, there were only 18 positive hits: 13 staff members and five students. At mobile testing units at schools near Brooklyn and Queens neighborhoods that have had new outbreaks, only four positive cases have turned up on 3,300 tests. In September, New York became the first big urban district to reopen schools for in-person learning, opening the doors to 1.1 million public-school students. Roughly half of the city’s students have opted for hybrid learning, in which they are in the building for just a few days a week. The approach has enabled the city to keep class sizes small and create more space between desks.