When it comes to assessing threats, New York City and Los Angeles schools likely have more experience than most other districts in the country.

But their reactions were dramatically different Tuesday to the same threat of a large-scale jihadi attack with guns and bombs — LA dismissed all its classes while New York dismissed the warning as a hoax.

The divergent responses from the nation's two biggest K-12 public school systems reflected what many in school security know: That deciding whether or not a threat is credible is hardly a mathematical process and the stakes in staying open or closing are high. It is one that school district officials around the country have weighed heavily in the wake of school shootings and terrorist threats.

Across the nation, small and large districts regularly encounter the age-old challenge of deciphering threats, complicated today by more sophisticated technology that can make them harder to trace.

Even when a threat is determined to be a hoax, the consequences can be a severe, with the safety of thousands of children, millions of school funding, and the message each decision sends on the line.

It's extremely rare for a major U.S. city to close all its schools because of a threat and it reflected the lingering unease in Southern California following the terrorist attack that killed 14 people at a holiday luncheon two weeks ago in San Bernardino.

"If this was not ISIS, not a terror organization, they're nonetheless watching," Rep. Adam Schiff, D-Calif., said Wednesday on MSNBC's "Meet the Press Daily." "And if they come to the conclusion that they can literally mail it in, call it in and disrupt large cities, they're going to take advantage of that."

A 2014 analysis by National School Safety and Security Services, a Cleveland-based consulting firm, found a 158 percent increase in the number of threats schools received over the previous year. About 37 percent of the threats were sent electronically and nearly a third resulted in schools being evacuated. Nearly 10 percent of the threats closed school for at least one day.

Ken Trump, president of the firm, said schools leaders faced with a threat they don't believe is credible sometimes let community anxiety rule the decision to evacuate or close, even though children might be safer in school than sent home where they could be left unsupervised.

"It's often better to keep them in school," he said.

In LA, the threat came in the form of an email to a school board member. Authorities in New York reported receiving the same "generic" email and decided there was no danger to schoolchildren. Mayor Bill de Blasio concluded the threat contained "nothing credible." New York Police Commissioner William Bratton said that it looked like the sender of the threat had watched a lot of the Showtime terrorism drama "Homeland."

Los Angeles officials announced Tuesday evening that schools would reopen Wednesday, with all city police officers ordered to be in uniform and extra patrol at schools.

Officials in LA defended the move to shut down its entire district, with that city's police chief dismissing the criticism as "irresponsible."

"We have suffered too many school shootings in America to ignore these kinds of threats," Chief Charlie Beck said.

Victor Asal, chair of public administration at the State University of New York at Albany, said the decision each district made was reflective of their respective experiences. New York has invested heavily in homeland security and terrorism response, which might make it easier to process how big a threat is, he said.

"Los Angeles doesn't have that same kind of experience," he said. "So you take the investment New York has and you take the nervousness that Los Angeles is feeling because it's an hour away from San Bernardino, and that creates a situation where I would expect the two cities to react differently."

LA schools commonly get threats, but Los Angeles Superintendent Ramon Cortines called this one rare and said the San Bernardino attack influenced his decision to close the entire district.

The threat "was not to one school, two schools or three schools," he said at a news conference Tuesday morning. "It was many schools, not specifically identified. ... That's the reason I took the action that I did."

The threat disrupted the routines of many Los Angeles families and sparked nerves in a region already on edge.

Lupita Vela, who has a daughter in the third grade and a son who is a high school senior, called the threat "absolutely terrifying" in light of the San Bernardino attack.

"I don't want this to be in the back of her head," she said. "Who knows what it does psychologically to kids? Is this going to cause her some kind of trauma so that she's not going to feel safe at school?"

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Associated Press writers Tami Abdollah in Washington and Christopher Weber, Amanda Lee Myers, Michael Blood and Edwin Tamara in Los Angeles contributed to this report.