LOS ANGELES (CNS) — Hundreds of thousands of Los Angeles Unified School District students returned to classrooms Monday, but some were met with long lines as they arrived on campus due to an extended process of verifying requiring COVID-19 tests.

Some parents took to social media to complain about long delays on campuses, contending the Daily Pass app that allows students to quickly report any health issues and show proof of COVID test results had crashed. Others said many other parents simply didn't know how to use the system, causing delays.

Interim Superintendent Megan K. Reilly acknowledged issues with the Daily Pass system, attributing it to the sheer number of people accessing it on the first day of classes.

"People were understanding about what was occurring," Reilly told KNX Newsradio. "The Daily Pass was slow, but we are working with the people about ... the volume. I think the volume of students coming back has been really a gratifying thing."

Long lines of students were seen outside John Marshall, Narbonne and Los Angeles high schools as students waited to be screened so they could enter the campus. Another campus had a long line of students, who apparently had not been tested in advance, waiting to undergo rapid COVID testing so they could enter classrooms.

All LAUSD students, teachers and staff are required to undergo weekly COVID-19 testing. All district employees have until Oct. 15 to be fully vaccinated against COVID-19 or face possible termination.

"I think all of us know inside that this year will be, again, unlike any other," interim Superintendent Megan K. Reilly said in a back-to-school speech last week.

While the year will be a stark contrast to 2020, when all learning was done remotely, the district's return to full in-person instruction comes in the shadow of growing concerns about the highly infectious Delta variant of COVID-19 that has sent L.A. County case numbers and hospitalizations soaring in recent weeks.

In her speech last week, Reilly said the new school year comes as people look to "retake the reins" of their lives from COVID. But the virus will be unforgettably present as classes resume.

Mask-wearing will be required by students and staff, regular cleaning and sanitizing will be conducted on campuses, with frequent hand-washing and social distancing encouraged. The district has also repeatedly highlighted upgraded air-filtration systems on campuses.

In announcing the vaccination requirement for employees last week, Reilly said "the science is clear" that the shots are the best protection against the virus.

"To date, our safety measures include daily health checks for everyone going onto school campuses, masks, comprehensive COVID-19 testing, contact tracing and isolation of cases, hand sanitizer, increased sanitization/cleaning of schools and upgraded ventilation," she said. "This additional step goes above local and federal health guidelines in order to provide another layer of safety in our schools, especially for our youngest learners.

"We deeply care about all of our employees. We appreciate everyone's commitment to maintaining the safest possible environment for the students and families we serve."

The requirement goes beyond orders issued by the state last week, requiring all public and private school employees to either show proof of vaccination or undergo weekly testing.

United Teachers Los Angeles, the union representing LAUSD educators, threw its support behind the mandate. The union's board, which previously voted not to oppose a mandate, toughened its stance last week and voted in favor of a vaccine mandate.

"I am the parent of an LAUSD fifth-grader, and my family has been going through the same uncertainty and anguish as so many other families as we approach the return to school," UTLA President Cecily Myart-Cruz said.

"Because of the protocols that UTLA educators and LAUSD families fought for and won, LA Unified has among the strictest COVID safety protocols in the country. But this Delta variant is unlike anything we have seen so far in this crisis — especially its impact on children — and we all need to step up to do our part to protect the most vulnerable among us."

The LAUSD is the second-largest school district in the nation, behind only New York.

Although in-person instruction will be the norm as classes resume, the district offered an online option for students unable or unwilling to return. According to the district, 12,456 students opted for the online learning, or less than 3% of the district's student enrollment.