BRUNSWICK, Maine (AP) — Chaz Wing was 12 when they came after him. The classmates who tormented him were children, too, entering the age of pimples and cracking voices.

Eventually, he swore under oath, the boys raped him and left him bleeding, the culmination of a year of harassment. Though Chaz repeatedly told teachers and administrators about insults and physical attacks, he didn't report being sexually assaulted until a year later, launching a long legal fight over whether his school had done enough to protect him.

Chaz's saga is more than a tale of escalating bullying. Across the U.S., thousands of students have been sexually assaulted, by other students, in high schools, junior highs and even elementary schools — a hidden horror educators have long been warned not to ignore.

Relying on state education records, supplemented by federal crime data, a yearlong investigation by The Associated Press uncovered roughly 17,000 official reports of sex assaults by students over a four-year period, from fall 2011 to spring 2015.

Though that figure represents the most complete tally yet of sexual assaults among the nation's 50 million K-12 students, it does not fully capture the problem because such attacks are greatly under-reported, some states don't track them and those that do vary widely in how they classify and catalog sexual violence. A number of academic estimates range sharply higher.

"Schools are required to keep students safe," said Charol Shakeshaft, a Virginia Commonwealth University professor who specializes in school sexual misconduct. "It is part of their mission. It is part of their legal responsibility. It isn't happening. Why don't we know more about it, and why isn't it being stopped?"

Elementary and secondary schools have no national requirement to track or disclose sexual violence, and they feel tremendous pressure to hide it. Even under varying state laws, acknowledging an incident can trigger liabilities and requirements to act.

And when schools don't act — or when their efforts to root out abuse are ineffectual — justice is not served.

This, Chaz Wing said in his lawsuit against the Brunswick school district, is precisely what happened to him.

Though the school contests whether any rapes occurred, the AP found that school administrators allowed Chaz's bullying to escalate and then failed to adequately investigate his allegations of sexual abuse.

From almost his first day at Brunswick Junior High, Chaz said kids harassed him, taunted him about his weight and subjected him to ordeals like a "gay test." Complaining to teachers and administrators didn't help, he said. He slid into depression and refused to go to school.

Then one day in 2012, his mom came home and found him curled up in her bed, rocking back and forth. She begged him to tell her what was wrong. Slowly, his words came out.

"They hurt me," he cried.

He said he'd been raped. Three times.

Chaz told police, child-abuse investigators and lawyers under oath that he kept quiet about the assaults for nearly a year because of threats against him and his family if he talked.

Sexual abuse allegations can be difficult to investigate. Because many accusers initially keep quiet, physical evidence can be long gone once investigators step in. Often, there are no eyewitnesses, leaving only the conflicting accounts of the accuser and the accused.

What Chaz told authorities and investigators — multiple times over four years — remained consistent, an AP review of government and court records shows. And a child-abuse examiner wrote of "strong evidence" that Chaz was sexually assaulted.

The school district staunchly defends how it handled its investigation. The junior high principal said his inquiry determined that the sexual assaults were "very unlikely." One of the accused boys, he noted, had never even heard of anal rape.

"There is — as there should be — always an inclination to believe allegations of sexual assault at the outset," district lawyer Melissa Hewey said in an email to AP. "But sometimes, the evidence compels the conclusion that those allegations are false."

"The little boys who were accused," she said, "are the real victims in this case and they deserve to be protected."

A HIDDEN PROBLEM

Children remain most vulnerable to sexual assaults by other children in the privacy of a home, according to AP's review of the federal crime data, which allowed for a more detailed analysis than state education records. But schools — where many more adults are keeping watch, and where parents trust their kids will be kept safe — are the No. 2 site where juveniles are sexually violated by their peers.

Ranging from rape and sodomy to forced oral sex and fondling, the sexual violence that AP tracked often was mischaracterized as bullying, hazing or consensual behavior. It occurred anywhere students were left unsupervised: buses and bathrooms, hallways and locker rooms. No type of school was immune, whether it be in an upper-class suburb, an inner-city neighborhood or a blue-collar farm town.

And all types of children were vulnerable, not just kids like Chaz who have trouble fitting in.

Unwanted fondling was the most common form of assault, but about one in five of the students assaulted were raped, sodomized or penetrated with an object, according to AP's analysis of the federal incident-based crime data.

About 5 percent of the sexual violence involved 5- and 6-year-olds . But the numbers increased significantly between ages 10 and 11 — about the time many students start their middle-school years — and continued rising up until age 14. They then dropped as students progressed through their high school years.

The AP counted only the most severe forms of sexual assault, excluding categories that were more broadly termed, such as sexual harassment, or behavior like kissing on the playground.

Contrary to public perception, data showed that student sexual assaults by peers were far more common than those by teachers. For every adult-on-child sexual attack reported on school property, there were seven assaults by students, AP's analysis of the federal crime data showed.

Schools frequently were unwilling or ill-equipped to address the problem, AP found, despite having long been warned by the U.S. Supreme Court that they could be liable for monetary damages. Some administrators and educators even engaged in cover-ups to hide evidence of a possible crime and protect their schools' image.

"No principal wants their school to be the rape school, to be listed in the newspaper as being investigated. Schools try to bury it. It's the courageous principal that does the right thing," said Dr. Bill Howe, a former K-12 teacher who spent 17 years overseeing Connecticut's state compliance with Title IX, the federal law used to help protect victims of sexual assault in schools.

Laws and legal hurdles also favor silence. Schools have broadly interpreted rules protecting student and juvenile privacy to withhold basic information about sexual attacks from their communities. Victims and their families face high legal thresholds to successfully sue school districts for not maintaining safe learning environments.

"Everyone feels like we don't have a problem, and the reason they feel that way is they have their heads in the sand," said Oregon psychologist Wilson Kenney, who has helped develop student intervention programs.

Student-on-student sexual assaults live in the shadows compared to the attention paid to gun violence in schools, most notably the Newtown shooting, Kenney noted. "There's no Sandy Hook for sexual misconduct. But I think the potential harm is great," he said.

Chaz's legal fight with Brunswick Junior High offers a rare insight into a school investigation of student sexual assault allegations.

The AP reviewed about 1,500 pages of sworn testimony, emails, court documents and investigative reports, as well as videotaped depositions of 15 school administrators, teachers and police, and interviews with a dozen people tied to the case.

School and district officials declined AP's interview requests. So did parents of some of the students accused in the attacks, except to say their sons were innocent.

The AP does not usually name alleged victims of sexual assault, but Chaz and his parents decided to speak publicly in hopes of helping others.

"I don't want this to happen to other kids," said his mom, Amy Wing.

WARNING SIGNS

From Chaz's first days at Brunswick Junior High in September 2010, teachers say it was clear he was the type of kid bullies would target.

Overweight with a brown mullet, he had unpopular opinions and wasn't shy about expressing them. He despised sports, video games and pop music. When other boys showed up for a class project in soccer jerseys, he displayed his love of gardening by wearing a hat and gloves, carrying a trowel and handing out flower-shaped sugar cookies.

Early on, Chaz testified in his lawsuit, several boys cornered him at his locker, mocking him and calling him fat. What bothered him most, though, was the "gay test." Feeling a light touch on his shoulder in social studies class, he brushed off a boy's hand. Seconds later, it was back. It was a test, he was told: If he didn't notice for 10 seconds, he must like it and be gay. Before long, half the boys in the class were doing it.

"Why are they so mean?" Chaz often asked Amy when he came home. "Why do they hate me?"

Initially, Amy urged him to ignore the bullying and try to get along with others. But after the "gay test" began, she also encouraged him to report incidents as they happened and so he did, dozens and dozens of times to teachers, his guidance counselor and the principal. He complained so often that he came to be seen as an overly sensitive nuisance.

One teacher asked Chaz if he was gay, he testified. "I told her 'no' and she said then don't worry about it."

Finally, Chaz made an appointment to see the principal, Walter Wallace, who had formed an anti-bullying committee shortly after joining the school. In early 2010, Wallace testified, Brunswick students had participated in a survey in which 1 in 6 pupils reported being regularly physically victimized. Wallace implemented a system for documenting student abuse, but it recorded only complaints that were confirmed and then only in the files of the accused, not the victim.

In their meeting in late 2010, Chaz said he detailed the harassment — but the problems continued. Wallace later testified he spoke to the boys Chaz identified and "never heard about it again." But Chaz said another wave started with a different set of boys.

By January 2011, losing patience, Amy first met with Wallace. "It needs to stop," she told him. Two weeks later, as the bullying continued, she was back in his office.

Wallace later told her he'd talked to the four main instigators and at least one acknowledged taking part in the "gay test."

Chaz entered Brunswick Junior High with a "gifted and talented" designation, but by the time he started seventh grade in fall 2011, his academic marks had dropped. His harassment complaints were consuming so much of teachers' time that they asked Wallace and his vice principal to take over.

"It wasn't happening when we were watching and we were trying to keep a close eye on it," one teacher testified, "but it was always around the corner and away from us."

The principal said he thought Chaz was becoming overly sensitive and made many reports teachers could not substantiate. But Chaz's seventh-grade counselor, Bunny Andrews, testified that she became "very, very concerned" as incidents began to pile up.

"Chaz was bullied," she said. "I could never deny that."

Then the physical torment he was experiencing escalated dramatically, Chaz testified: In November 2011, he said, he was sexually assaulted by classmates for the first time.

According to the lawsuit, the boys crawled under the door of the bathroom stall, put the blade of a small knife against his wrist, ordered him to the ground and overpowered him. After they raped him, Chaz said, one boy threatened to burn down his house, harm his family and kill his pets if anyone found out — then sliced into his right arm.

By the following February, Amy noticed Chaz was stressed and unable to complete his work, so she contacted the school.

That was around the time Chaz said he was raped again. He testified he had been changing clothes for gym in a locker-room stall because he felt self-conscious about his looks. A different boy pushed his way in past a broken lock as a second boy stood guard outside.

The boy forced him against the wall and ripped down his shorts, Chaz said, and it was over in less than two minutes. He stayed silent, he said, cowed by the threats of the first assault.

One day in late spring — Chaz can't recall whether it was April or May — the school's power went out shortly before lunch so he left class early to beat the crowd to the cafeteria. As he passed a bathroom, he testified, he was grabbed from behind, dragged inside and pinned against the back wall. It was too dark to see his attackers, but he felt a boy on either side hold his arms. After they finished raping him, he said, he stuffed toilet paper in his underwear to stop the bleeding.

Again, Chaz didn't speak out, he said, because he was afraid.

Still, records show the school knew Chaz's bullying had become more physical, including an attack he reported in which he was stabbed with a pencil, with the lead breaking off in his arm.

In June, school officials created a safety plan that included a teacher escorting him between classes. Two days later, after others gave him grief, Chaz told his escort, "Please, just don't. This is making things worse."

By the end of seventh grade, Chaz was missing days of class and easily agitated and angry. Amy called a lawyer at a non-profit defense fund who thought Chaz might have a case because he was bullied over his perceived sexuality.

On the last day of class, Amy marched into the school district's office for a copy of its anti-bullying policy. Two weeks later, she filed a complaint with the Maine Human Rights Commission — kicking off the legal fight that lasted more than four years.

OBLIGATED TO ACT

Studies have long found bullying can be a precursor to sexual harassment and assault. Typically, victims' grades drop, attendance falls and rates of depression, anxiety and suicidal thoughts increase. Schools sometimes miss the warning signs, though, and think it's just "kids being kids."

"There's just a reluctance to see that there's sexual violence at such a young age," said Dorothy Espelage, who researched sexual offenses and harassment among middle schoolers while at the University of Illinois.

In October 2010 and April 2011, the U.S. Education Department reminded public school districts that Title IX obligates them to act on bullying and sexual violence. They are required to investigate — separate from any police inquiry — and take prompt action. The department specifically called out anti-gay slurs, sexual remarks, physical harm and unwanted touching — much of what Chaz testified he was telling school officials.

School districts have had to report all sorts of data about students, from those who received free lunches to those who brought in firearms. But there is no federal mandate to track sexual violence.

By contrast, colleges and universities must keep a public crime log, send emergency alerts about sexual assaults, train staff and aid victims under a federal law named for a student who was raped and murdered in 1986.

"Obviously, we care enough to make colleges report," said Kansas City, Mo., lawyer Chris Dove, who has represented peer sex-abuse victims. "Shouldn't we care even more about kids under 18?"

Whether — and how — school sexual violence is tracked is determined by individual states, AP found, with wide variations in whether that information is verified or any training on student-on-student sexual assault is required. A survey of state education departments found:

—32 states and the District of Columbia track student sexual assaults, though some did so only if incidents led to discipline like suspension or expulsion; the other states, including Maine, did not.

—18 states reported they had training requirements for teachers, school administrators or students about peer-on-peer sex assault.

—Some of the nation's largest school districts reported zero sexual assaults over a multi-year period, and some state education officials told AP they doubted their districts' numbers.

In multiple cases, AP found that school districts bungled investigations, failed to supervise students they knew were trouble, neglected to inform authorities or worse.

A Mississippi high school failed to secure a computer lab that was the scene of a girl's alleged rape in 2014 and janitors cleaned it before law enforcement could collect evidence, according to court records. District lawyers said that happened because the girl didn't initially say the sex was forced. The three boys accused were suspended but returned to class days later.

A Missouri middle-school boy with a disciplinary record of groping girls fondled a female student on a school bus in 2014 and told a school official, "I can't seem to stop," according to a police report. When he moved to the district's high school the next year, he allegedly assaulted a girl in a classroom, police said. The boy claimed it was consensual and was initially suspended for 10 days, but later was charged with second-degree rape, the report said.

And in Iowa in 2013, parents didn't report their daughter's allegations of sexual assault to authorities because the elementary school principal indicated he would do so. They found out months later that didn't happen when they sought the police case number, according to the family's lawsuit. The parents then contacted authorities, and a sheriff's investigator took over. The results of his findings in the juvenile case are confidential.

When schools mishandle such cases, victims often have little recourse. Prosecutors are sometimes reluctant to charge kids, and clearing legal hurdles to sue districts is difficult.

A federal court in Alabama blocked the case of a 14-year-old girl who said she was used as "rape bait" and assaulted in 2010 in a botched plan to catch a boy suspected of sexual misconduct. Her case did not meet the legal standards to hold the school district liable, the judge wrote, even though he said the plan, devised by a middle school teacher's aide, was "foolish" and backfired "horribly." The ruling was successfully appealed, and the district ultimately settled for $200,000.

Settlement amounts can be so low that lawyers are reluctant to take on what are typically lengthy, complicated cases. For families, the painful and costly process usually is driven by more than a desire for money.

"The notion of holding schools accountable and making sure they make changes to address sexual assault is very important to victims," said Adele Kimmel , a lawyer with the Washington, D.C., legal nonprofit Public Justice.

THE INVESTIGATION

Chaz's eighth-grade year had begun well but, as the bullying flared again, he stopped attending school. When he finally told his mom in October 2012 that he had been sexually abused, she called school officials to say Chaz would not be returning to Brunswick.

Wallace, the principal, was out of town but alerted his boss, Superintendent Paul Perzanoski. The superintendent said in a deposition that he had not known bullies were targeting Chaz until Amy picked up the anti-bullying policy.

Instead of bringing in an experienced investigator, Perzanoski testified that he decided the junior high administrators could handle it. Wallace led the case with the help of Vice Principal Lisa Cushman — the same two people who were tasked with stopping Chaz's bullying. Neither had investigated a sexual assault before or had Title IX training.

Cushman interviewed Chaz, with his mom and his guidance counselor present.

And Wallace spoke to the four boys Chaz had identified as playing a role in the attacks, in the presence of their parents and a Brunswick police officer assigned to the school, Mike Andreotti, who later testified the principal hadn't kept him informed of Chaz's bullying complaints.

Under Education Department guidelines, schools are to conduct their own investigations separate from police inquiries. But, in his deposition, Wallace said he directed the questioning of the four boys, even though it was Andreotti's only meeting with the accused.

"It was very strong denials or it was confusion," Wallace said of the boys' responses. One, he said, "had no frame of reference for anal sex."

Wallace testified he surveyed the scenes where Chaz said the attacks took place. He also talked to a coach, who said that based on the space, location and the five to eight minutes boys had before gym, it would be virtually impossible to carry out a rape.

Wallace told Perzanoski the sexual assaults were "unlikely," but did not submit a written report. He never interviewed Chaz or talked to his parents about his findings. Instead, he emailed the Wings to say Chaz should return to school.

The school resource officer did interview Chaz, over 90 minutes at the police station. Unlike the interview with the accused boys, Chaz's parents were told to wait outside. Andreotti testified that he wasn't sure if they might be part of the problem — even though, Amy noted, they were the ones who had called police.

Andreotti told Chaz's parents he would conduct follow-up interviews with the four boys, but he did not do so after deciding there wasn't credible evidence of a sexual assault. Prosecutors agreed.

During his deposition, Andreotti was asked whether his viewpoint was changed by a child abuse evaluation he requested, which said Chaz's statements "were clear, consistent and provided idiosyncratic and sensory details" and found "strong evidence" Chaz had been sexually assaulted.

"Absolutely," Andreotti said, but he added that a physical examination had found no evidence of recent abuse or trauma. A lawyer for Chaz noted the examiner also said such an absence did not mean abuse didn't occur.

"That's correct. It's leaving the option open that it could have occurred," Andreotti replied.

The retired police officer declined AP's requests for an interview. Brunswick police also declined to discuss Chaz's case or provide a copy of its investigative report, saying juvenile cases were confidential under state law.

Andreotti had interviewed about 20 students and teachers and his investigation was "thorough," said Commander Mark Waltz, a police spokesman.

"It was all presented to the DA's office, and there were good reasons they made the decision that they did," Waltz said, refusing to elaborate. The Cumberland County district attorney's office declined comment.

To file suit, the Wings needed to convince the Human Rights Commission that Chaz was harassed over his perceived sexuality, that his learning environment turned hostile and that the school knew yet failed to take prompt, appropriate action.

The district said in filings to the commission that the school had taken Chaz's complaints seriously and argued Chaz's perception often "did not line up with the reality of the events," such as the time he reported one of his main bullies hit him with a lacrosse stick. The boy "credibly stated that he tapped" Chaz to say hello, the district said.

Lawyers for the district also alleged Chaz quit coming to class in an attempt to bolster his complaint. In fact, he had been hospitalized in December 2012 — the first of four times — diagnosed with depression, suicidal thoughts and PTSD and told not to return to Brunswick.

In June 2014, the commission's investigator found reasonable grounds to believe the district had discriminated against Chaz. She said the school district failed to see the "overall picture" of bullying and allowed "a hostile education environment to persist." But she reached no conclusion on the reported rapes because, she said, the other harassment was sufficient for her finding. She also noted that the scar on Chaz's arm and his ongoing treatment for depression "tend to support his allegations."

While the school "had good policies in place ... it did not do enough," in part by handling each incident on a case-by-case basis.

One month later, the commission cleared the way for the Wings to sue, which Amy did in July 2015, alleging Title IX violations. The commission joined as a co-plaintiff, it said, "to ensure that Brunswick has in place effective measures to prevent a hostile education environment based on sex and sexual orientation."

The district's lawyers aggressively quizzed Chaz during his eight-hour deposition. "How long was the first one on top of you?" one lawyer asked. "You just did what he asked you to do?"

As the judge neared a decision on whether the case could proceed to trial, the two sides considered a settlement. Weeks of negotiation led to a deal in the fall of 2016: The lawsuit would end, Brunswick would fix some of the tracking flaws that Chaz's case exposed, and Chaz would get $50,000.

There would not be an apology — one of the things that Chaz had wanted most.

Perzanoski declined AP's repeated requests to meet with him, Wallace and others involved in Chaz's case. He offered only a brief email comment, saying a major reason for the settlement was to allow everyone "to put the matter behind them and move forward."

SEASON OF HOPE

Chaz and Amy mark progress by the seasons: Last year, for the first time since telling his mom he'd been raped, he didn't spend part of the fall in a hospital.

"The fall is always a hard time for me every year," Chaz said, "because that's the time that the first assault happened. That's the time when I was finally able to tell my mom about what had happened. It's also the time that I left Brunswick Junior High School."

Amy sold the home with the big backyard across the street from her folks where Chaz and his brother had lived all their lives and moved to a nearby town so the boys could attend a different school.

Chaz continued to miss class his first two years at his new technology and science high school, where he received specialized instruction because of his depression and PTSD. After changing medication, he missed fewer classes. He sees a counselor every other week.

He is one of the youngest owners of a booth at a local flea market, where he chats with weekend visitors about his stash of old rotary phones, TVs, and other vintage electronics. He also works part time at a radio station, reading the weather and selling ads, and thinks he might like a career in broadcasting.

In a few weeks, Chaz turns 18 and will graduate. He'd always sworn he'd never leave Maine. Recently, though, he's been thinking about studying or working out of state. It's a sign his horizons may be widening.

"I'm still not really sure what I'll do," Chaz said. "Life is an open road."

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McDowell reported from Brunswick; Dunklin and Schmall from Dallas; Pritchard from Los Angeles. Associated Press writer Michelle R. Smith in Providence, Rhode Island, and AP researcher Rhonda Shafner in New York contributed to this report.

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If you have a tip, comment or story to share about student-on-student sexual assault at K-12 schools, please email: schoolhousesexassault@ap.org

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To follow or contact the reporters on Twitter: https://twitter.com/reesedunklin and https://twitter.com/emilyschmall and https://twitter.com/lalanewsman and https://twitter.com/robinmcdowell