An elementary school principal trying to prevent student walkouts during immigration rallies introduced a lockdown so strict that children weren't allowed to go to the bathroom, and instead had to use buckets in the classroom.

Worthington Elementary School Principal Angie Marquez imposed the lockdown March 27 as nearly 40,000 students across Southern California left classes to attend immigrants' rights demonstrations.

Marquez apparently misread the district handbook and ordered a lockdown designed for nuclear attacks.

Tim Brown, the district's director of operations, confirmed some students used buckets but said the principal's order to impose the most severe type of lockdown was an "honest mistake."

"When there's a nuclear attack, that's when buckets are used," Brown told the Times. The principal "followed procedure. She made a decision to follow the handbook. She just misread it."

A message left by The Associated Press for the principal at the school before business hours Monday was not immediately returned, and Marquez did not return telephone calls from the Los Angeles Times.

Appalled parents have complained to the school board. Brown said the school district planned to update its emergency preparedness instructions to give more explicit directions.

Parents and community activists asked the school board at its April 5 meeting to explain the principal's decision. They also sought promises that the lockdown wouldn't be repeated.

"There was no violence at the protests, so this was based on what?" activist Diane Sambrano asked. "It was unsanitary, unnecessary and absolutely unacceptable."