LOS ANGELES—Tens of thousands of Los Angeles Unified School District (LAUSD) students headed back to classes Jan. 11 amid a dramatic countywide surge in COVID-19 cases, but officials continue to insist on the effectiveness of infection-control measures on campus. The district required all students and staff to be tested for COVID-19 before returning to in-person activities, even distributing thousands of take-home test kits to students since Friday. Students and employees have been getting tested at district and other sites, with the program encountering thousands of infections. According to the district’s website, more than 414,000 tests had been administered as of Sunday, and 62,000 positive cases had been detected, giving the district a positivity rate of about 15 percent. Interim Superintendent Megan K. Reilly told reporters last week that, while high, the district’s positivity rate is still below that of the county as a whole. As of Sunday, the county’s overall …