Parents from Miramonte Elementary School turn out to meet with the Los Angeles School Superintendent John Deasy in a private meeting at South Region High School in Los Angeles in 2013. (Francine Orr/AP)

When leaders at Prince George’s County Public Schools announced last week that a volunteer at Judge Sylvania W. Woods Elementary School had allegedly made videos of more than a dozen children performing sex acts, the system’s chief executive put the school’s principal on paid leave.

When Los Angeles school officials found out four years ago that a third-grade teacher had abused dozens of children, including feeding them semen in what he called a tasting game, the system’s superintendent removed all 128 of the school’s staffers — every one of the 88 teachers and 40 janitors, administrators and others.

Sexual-abuse scandals often lead school leaders to promise tighter screening of job applicants, but effective screening against potential abuse is difficult — bordering on impossible, many experts on abuse say. So the search for other ways to protect children has focused on how to create a watchful, but not overbearing, atmosphere inside schools.

Los Angeles Superintendent John Deasy — who ran the Prince George’s system from 2006 to 2008 — got plenty of criticism for his clean sweep at Miramonte Elementary. The teachers’ union accused him of casting suspicion on innocent, good employees, and some parents worried that the loss of beloved teachers would compound the damage that the scandal had caused to their children’s sense of security.

Deasy announces that the entire teaching staff of Miramonte Elementary School will be relocated in the wake of the arrests of two teachers in a child sexual abuse scandal in Los Angeles. (David McNew/Reuters)

Deasy said his housecleaning was designed not to put teachers under suspicion for abusing children, but to root out a “culture of silence” that had allowed an adult to commit such appalling acts for years. Deasy said the reluctance of other adults to question a colleague’s odd behavior put children at risk.

Many experts on educator sex abuse, eager to find a reliable way to persuade a school’s adults to come forward when something is amiss, have latched onto Deasy’s decision to swap out the staff as an example of how to sniff out predators on a school’s staff.

“Pedophiles won’t stay where they have no way to get at the kids,” said Charol Shakeshaft, a Virginia Commonwealth University professor who conducted the largest federal study to date of sex abuse by educators. “A vigilant school says, ‘We won’t let that happen’ and makes it clear that if adults in the school don’t report what they see, they may lose their jobs.”

When abuse scandals emerge, parents and politicians inevitably call on schools to tighten screening of people applying to be teachers or volunteers. But even the best screening filters out only abusers who already have been caught, said Nancy Oglesby, deputy commonwealth’s attorney in Henrico County, Va., who specializes in sexual-abuse cases.

“If they haven’t been convicted already, running a criminal check isn’t going to help,” she said. “In fact, people who sexually assault kids are usually very approachable, very trustworthy — they often have many of the traits we value in an excellent teacher. Our efforts need to be put more toward having plenty of watchful eyes in the school.”

Screenings are not a complete waste of time. They just have to be done in a more labor-intensive and expensive way — not just by running a standard $49 computer background check, but by rigorously interviewing past employers and colleagues, according to several child-abuse experts.

Deonte Carraway is charged with several counts of felony child pornography, sexual abuse of a minor and second-degree sexual offense. Police have identified 17 children so far they say were victimized. (Prince George's County Police Department)

“You’d be shocked how much you can find out if you do it properly and ask the previous employer very specifically, ‘Why did he leave? Was he ever suspected of sexual abuse behavior?’ ” said Deasy, who had 74,000 employees in the Los Angeles Unified School District. “Now you’ve created liability and the previous employer must answer.”

Too often, school leaders who have heard about suspicious behavior by a teacher — taking children into one-on-one lunchtime or after-school meetings in rooms with closed doors, or driving children home with no one else in the car — get rid of the problem by moving the teacher to another school, said Deasy, who left the Los Angeles system in 2014 and now consults for the Broad Center for the Management of School Systems, a nonprofit agency in Los Angeles.

“Too many schools still use the geographic fix we saw in the Catholic Church’s scandals, rather than outright firing the person,” Deasy said.

Asking the pointed question is very hard, he said: “It’s a topic people don’t talk about. No one wants to have to ask a teacher, ‘Did you touch a child’s genitals?’ ”

When Shakeshaft studied available data on abuse by teachers, she concluded that about 7 percent of U.S. students have experienced abuse without physical contact and about 9 percent have suffered abuse with contact. A much smaller percentage of teachers are abusers because most predators are chronic offenders.

A large-scale scandal at New York’s Horace Mann School, an elite private school where more than 20 teachers were accused four years ago of abusing more than 60 students over more than two decades, led to a wave of revelations at private schools. Many of those schools, unlike Horace Mann, commissioned independent investigations to learn what had happened and why.

Public schools have generally used abuse scandals as a moment to beef up screening and educate teachers and children about prevention, as Montgomery County did last year after former music teacher Lawrence Joynes, who taught for 27 years at 11 Montgomery schools, pleaded guilty to sexually abusing 15 minors at elementary and middle schools in Silver Spring. Some chronic abusers can go decades without getting caught, as former Manassas English teacher Kevin Ricks did, moving from one teaching job to the next over nearly three decades before being convicted and sentenced to 25 years in prison five years ago.

In the Prince George’s case, police said Deonte Carraway, 22, of Glenarden, has admitted making videos in which he directs children to perform sex acts; police have identified 17 victims and expect to find more. County schools chief executive Kevin Maxwell said he removed Woods Elementary’s principal, Michelle Williams, out of an “abundance of caution.”

The Los Angeles system ended up paying more than $169 million in the Miramonte case, settling lawsuits filed by 69 parents and 81 students who accused teacher Mark Berndt of lewd acts. Berndt, who was caught when a CVS drugstore photo technician saw his pictures of blindfolded children and alerted police, was sentenced to 25 years in prison. It turned out that several students had tried to alert adults about him, including two girls who had told a guidance counselor many years earlier that they saw Berndt masturbating behind his desk; the counselor told them to stop making up stories.

Deasy didn’t limit his sweep to the one school; he suspended or removed more than 300 teachers in the two years following Berndt’s arrest — most not for committing abuse themselves but for failing to report suspicious behavior by colleagues.

“Without the slightest reservation, you tear the place apart, looking at records, at people, at training,” Deasy said. “We have no problem sitting down with a parent and saying your child is misbehaving. Yet we have an enormous problem sitting down with faculty and saying, ‘These are the rules and you must be watching for this behavior in your school.’ ”

Deasy concedes that there is a danger of overcorrecting for a scandal. He offers the zero-tolerance craze of the past decade as an example of schools overcriminalizing children’s misbehavior. But he says sexual abuse is different because its victims are affected for the rest of their lives.

Union leaders told Deasy that by instantly removing teachers from classrooms after unsubstantiated reports of suspicious behavior, he was endangering the careers of innocent teachers. And some abuse experts argue that sexual-offender registries, which tag people forever, have had a chilling effect, making people extremely reluctant to report suspicious behavior for fear of doing unjustified and permanent damage to a co-worker’s reputation.

“Some of the steps schools have taken are extreme — telling teachers never to be alone with a student or never to hug a student,” said Janet Rosenzweig, vice president of Prevent Child Abuse America and an adviser to schools and parents on dealing with sexual abuse. “An air of paranoia permeates a lot of our institutions. The answer is to teach kids how to be alone with a teacher and allow these perfectly wonderful, normal relationships, with clear boundaries.”

Shakeshaft, concerned about the danger of overreactions, conducted a study tracing what happened to teachers who were falsely accused of abuse. “All of them had jobs, and it wasn’t a big universe,” she said. “Schools have to know how to handle suspicions quietly. You don’t alert the whole school. If you’re smart about it, you can clear someone of suspicion in a matter of hours.”

The other side of that coin, though, is that teachers have to be willing to report what they’re hearing. “Too often when kids say ‘this teacher’s weird’ or they’re seeing this teacher at the mall with girls with long blond hair, the other teachers ignore it or think it’s just kid talk,” Shakeshaft said.

Many teachers are reluctant to call out behaviors that are often associated with effective teaching — paying extra attention to needy kids, for example. That’s why schools should set rules that, for example, encourage individual attention but ask that it take place in a corner of the library or cafeteria rather than alone behind a closed door, abuse experts said.

At Miramonte, “Deasy got that something was rotten in the atmosphere of the school,” Rosenzweig said. “The adults in the building have to be taught that it’s not enough to have good or bad people; you have to maintain a healthy sexual environment. That means every teacher has to define the norms — set a dress code, talk about what kind of language is acceptable, talk about how teachers talk to kids.”

Sexual arousal is natural and inevitable when young adults are teaching adolescents, Rosenzweig said. The school’s job is to build an atmosphere in which acting on such impulses is both unacceptable and practically difficult. “All of a sudden, Mr. or Ms. Mediocre in high school is now getting up in front of kids with hormones raging and they’re the queen bee for the first time,” she said. “We’ve got our heads in the sand about this. We have to talk about it and then set boundaries for teacher behavior.”

In the Los Angeles case, the removed staffers were relocated for the rest of the year and returned to Miramonte the next fall with extensive retraining on their responsibilities to report unusual student-teacher contact.

Deasy said some people still complain that he overreacted, but he said he wouldn’t do anything differently. When he first met with parents at Miramonte, “I couldn’t tell them I am absolutely sure there’s nobody here who’s a danger,” he recalled. “And the teachers felt guilt too: ‘How could I not have known?’ The only answer was to change the culture of the place. It’s the most difficult thing to talk about, but you have to speak to every employee in very explicit, uncomfortable language. It’s the hardest thing I’ve ever dealt with.”