This week New York City’s public schools will close their doors and students will once again undertake online instruction. The shutdown was triggered when 3 percent of coronavirus tests in the city came back positive over seven days. There are questions, however, around this number being used as a trigger — some health officials maintain that schools are safe. When is the right time for schools to reopen and what is the right threshold for closures? We explore what lessons New York City’s struggles hold for the rest of the nation. Guest: Eliza Shapiro, who covers New York City education for The New York Times, walks us through the city’s decision to reopen schools and the difficult decision to shut them down.  We want to hear from you. Fill out our survey about The Daily and other shows at: nytimes.com/thedailysurvey For more information on today’s episode, visit nytimes.com/thedaily  Background reading: New York City’s public school system will close this week, moving to all-remote instruction and disrupting the education of roughly 300,000 children.As schools close again, frustrated and angry parents say the decision does not make the city safer.