Coronavirus cases are already surfacing in K-12 schools that have reopened, but the federal government is not tracking these outbreaks, and some states are not publicly reporting them, making it more difficult to determine how the virus is spreading, experts say. Scores of students and staff members have been quarantined because of potential COVID-19 exposure in Georgia, Alabama, Mississippi and Indiana, among other states. But there is no official national tally of school-linked COVID-19 cases, and some states are not reporting how many outbreaks have occurred or how many students and staff members have been infected.