Amid public alarm over the inadequacy of coronavirus testing across the nation, Los Angeles schools on Monday will begin a sweeping program to test hundreds of thousands of students and teachers as the nation’s second-largest school district goes back to school — online.

The program, which will be rolled out over the next few months by the Los Angeles Unified School District, will administer tests to nearly 700,000 students and 75,000 employees as the district awaits permission from public health authorities to resume in-person instruction, said Austin Beutner, the district’s superintendent.

It appears to be the most ambitious testing initiative so far among major public school districts, most of which are also starting school remotely but have yet to announce detailed testing plans…

Public health experts have said that expanded coronavirus testing, with rapid results, is the key to curbing the spread of the virus, particularly in schools, where teachers and students mingle regularly in close quarters. Six months into the pandemic, however, testing remains a persistent hurdle, with backlogs and other issues at state health departments, including California’s, and long wait times in some areas for test results.