View of the Washington, DC, campus of the Sidwell Friends School {Photo by Nicholas Kamm/AFP/Getty Images) (NICHOLAS KAMM/AFP/Getty Images)

Officials at Sidwell Friends School were quick to respond when they received a call recently that a longtime music teacher had been accused of sexually abusing a former student at another school two decades earlier.

Within a week, they had obtained a police report, confronted the teacher, met with attorneys and drafted a public statement that included an admission that an administrator who had offered Michael Henderson the job had known “boundaries had been crossed” in his previous job but hired him anyway.

A letter to the school community announcing Henderson’s dismissal apologized for the school’s “grave lapse in judgement” and encouraged current or former students, parents or employees to come forward and report any inappropriate behavior or abuse by anyone at the school.

Henderson, through his attorney, has denied any wrongdoing.

Sidwell’s statement — and the admission within it — represents an unusually detailed and public response for the discreet private school in Northwest Washington that has been attended by the children of U.S. presidents, including Sasha and Malia Obama. The move also signifies what advocates and attorneys describe as a sea change in how private schools are beginning to respond to allegations of sexual assault amid a series of high-profile scandals unfolding at some of the nation’s most prominent private schools.

“In the past, it was modus operandi: When there was an allegation, you covered it up,” said Kevin Mulhearn, a New York-based attorney who has represented dozens of abuse victims. Now, he said, there’s “another school of thought” emerging that emphasizes transparency and justice for victims.

News reports in recent years have exposed a pattern of abuse at many private schools, documenting serial abusers who went unchecked for years or were allowed to slip away quietly and were never reported to law enforcement or prospective future employers. Litigation is mounting at many schools, and alumni groups are organizing to press for greater transparency and justice for victims.

At the same time, more victims are feeling empowered to come forward, often after decades of silence, amid a broader cultural shift in how people view and understand sexual abuse and how it plays out in schools.

Many schools see addressing allegations directly and publicly, rather than hiding from them, as a way to reassure parents that their institutions can be trusted.

Ellis Turner, Sidwell’s associate head of school, said the school also encouraged members of the community in 2010 to report any information about possible abuse after a middle school teacher was found to have abused a student. “As a Friends school we have a special obligation to address such matters openly and honestly,” he said in a written statement. No one came forward, officials said.

In last week’s statement, Sidwell said its hiring practices have improved significantly over the past 20 years, but it also detailed some additional precautions the school is taking by retaining an employment law expert to analyze its practices and retaining independent counsel to review all past personnel files.

Many schools are rewriting handbooks, bringing in trainers to help school employees spot techniques that abusers use to groom their victims and developing curriculum for students about healthy relationships.

Dozens of private schools that have faced particularly grave allegations have commissioned independent external investigations to document past sexual abuse at their institutions, handing over reams of personnel files to teams of lawyers and submitting to scores of interviews with the goal of airing out their dark closets once and for all.

Last month, Choate Rosemary Hall, a Connecticut boarding school that counts John F. Kennedy among its alumni, published a report that documents sexual abuse by 12 former faculty members and includes detailed accounts of 24 victims between the 1950s and 2010.

“The conduct of these adults violated the foundation of our community: the sacred trust between students and the adults charged with their care,” wrote Michael J. Carr, chair of the board of trustees, and Alex Curtis, headmaster, in a letter that accompanied the report.

“On behalf of Choate Rosemary Hall, we profoundly apologize,” they wrote.

Also last month, Emma Willard, a girls boarding school in Upstate New York, issued a report documenting widespread sexual misconduct and abuse over the past 60 years.

Willard, as well as Choate, were featured in a Boston Globe investigation last year that found that at least 67 private schools in New England have faced accusations since 1991 that staff members sexually abused or harassed more than 200 students. Among the accused was a history teacher who was fired from Emma Willard in 1999 after he allegedly raped a student, then was given a letter of recommendation and went on to work at another private school.

“We are taking responsibility for the past so that our future is different,” said Elisabeth Allen LeFort, chair of the board of trustees, and Susan R. Groesbeck, interim head of school, in a letter released with the Emma Willard investigation.

Other schools have launched external investigations, though not published detailed reports, including Phillips Exeter Academy, the alma mater of Mark Zuckerberg, which came under scrutiny after the school admitted that it hid allegations of abuse by the former chair of the school’s history department and allowed him to quietly retire in 2011, a few years before another allegation surfaced.

Child sexual abuse occurs in public and private schools. But some experts say the culture of private schools — which tend to encourage close relationships between students and teachers — can foster a blurring of boundaries. And over the years, many private schools have been motivated by a strong desire to protect their elite reputations.

Paul Mones, an attorney who specializes in working with victims of sexual abuse, said it’s harder for outsiders to question independent school practices. “In private schools, the walls of silence are higher,” he said.

Boarding schools have particular challenges, with students far away from home and looking to other adults for emotional support.

The National Association of Independent Schools convened a task force this school year to help its 1,500 member schools respond to and prevent educator sexual misconduct, studying issues such as hiring practices, boundary setting and how reporting requirements vary by state.

“Schools have not known how to deal with this, and many have botched it,” said Charol Shakeshaft, a professor at Virginia Commonwealth University and an expert in educator sexual abuse, who is on the task force. “Now I see them saying, ‘We may be coming in too late . . . but that should not stop us from changing now.’ ”

Not all schools are opting for transparency. An alumni group from Horace Mann in New York commissioned its own external investigation after the board of trustees decided not to commission one, following reports in the New York Times and the New Yorker in 2012 and 2013 that exposed serial abuse by multiple teachers. And many schools still scuttle or fight claims, Mulhearn said.

Also, systemic hurdles discourage schools from reporting allegations to law enforcement, advocates say. Statutes of limitations for prosecuting sex crimes vary widely, in some states expiring not long after students graduate, creating an incentive for schools to delay investigations and run down the clock.

Michele Booth Cole, executive director of Safe Shores — The D.C. Children’s Advocacy Center, which serves young victims of abuse, said she is heartened to see more private schools addressing the issue of child sexual abuse. But she said more schools should act before they are dealing with a crisis.

Cole was the parent of a third-grader at the Beauvoir school in the District when her daughter’s teacher, Eric Toth, was escorted off campus following discovery of sexually explicit pictures he took of students. Toth fled. Cole said the school’s response led to extensive staff training to recognize the warning signs of sexual abuse and an overhaul of their policies to make the school safer.

“If schools would do what Beauvoir did after the fact, then that would protect a lot more kids from being abused,” she said.

Sara Lawson, the woman who with her boyfriend contacted Sidwell last month to inform them about her abuse allegations against Henderson, said she was “amazed” by the school’s response.

“Wow. Just wow,” she said, after she got off the phone with an attorney for the school who outlined some of the actions the school planned to take.

She said her conversation with the Sidwell attorney stood in stark contrast to the “grilling” she described going through in telling and retelling her story of her abuse to school officials at the Colorado boarding school where she met and, she said, was abused by her music teacher.

Henderson left the school, but criminal charges were never brought against him. She spent the next 20 years trying to “bury” what happened, she said.

When she recently learned that he had been teaching all along, she said the revelation made her feel guilty for not speaking out sooner or trying to track him down. It felt too hard, she said. But now that she has seen the results, she is glad that she did.

“I feel empowered,” she said, to see action in a part of her life that felt broken. “I never felt that before.”