The true extent of student-on-student sexual assault in elementary and secondary schools is unclear. There are no national requirements for schools to track and disclose such incidents, as there are for colleges and universities, and sexual violence in general is widely under-reported.

Even academic and government research on K-12 student sex assault has limitations. Some surveys focused on certain age groups, were limited by a school’s demographics or were dependent on what students were willing to report. Others did not distinguish between incidents on and off school property, or whether offenders included non-students.

Here are the results of some studies:

University of New Hampshire’s Crimes Against Children Research, 2014

A study published in 2014 by the University of New Hampshire’s Crimes Against Children Research Center found that one in 250 children said they had experienced forced or unwanted sexual contact at school in the past year. The study was based on surveys taken in 2011 of 3,391 children, ages 5 to 17.

Most of the 14 respondents who reported being sexual assaulted said a peer was the attacker, and just over half reported it to school officials. Researchers said the number of at-school assaults was likely an undercount and too small to calculate a reliable national estimate.

University of Illinois, 2014

University of Illinois researchers reported in a 2014 study that about one in five students from Midwestern middle schools said they had faced sexual violence on school property the previous year.

Students asked to describe the “most upsetting sexually violent act” discussed actions ranging from forced intimate touching to unwanted kissing. Roughly 1,400 boys and girls were surveyed in grades 5 through 8, but only about 60 percent answered all the questions.

The National Center for Education Statistics, 2014

The National Center for Education Statistics tried to estimate the number of rapes and sexual batteries in U.S. public schools in the 2013-14 school year. Principals were asked about violent incidents at their schools as of February 2014, regardless of whether a student or an adult committed them. More than 80 percent of the 1,600 public elementary, middle and high school principals surveyed participated.

In the end, nearly 2 percent of the administrators reported a sexual battery and less than one-half of 1 percent reported a rape or attempted rape. Researchers cautioned the response rate for some categories, including rape, was too small for a reliable national estimate. The center estimated that roughly 1,800 sexual batteries other than rape were reported.

American Association of University Women, 2011

Researchers with the American Association of University Women asked nearly 2,000 students in grades 7-12 nationwide about sexual harassment at their public or private schools during the 2010-11 academic year. Two percent reported being “forced to do something sexual,” and 8 percent said they were “touched in an unwelcome sexual way” — with girls experiencing much higher rates than boys.

The results did not specifically identify the perpetrator, but the study said nearly all the behavior it documented was peer-on-peer. Half said they did nothing after being “sexually harassed,” and a quarter said they told a relative. Just 9 percent said they told a teacher, counselor or other adult at school, and only 1 percent contacted police.

University of Michigan, 2008

University of Michigan researchers surveyed nearly 1,100 junior and high school students in the state about peer sexual assault, both in and out of school. The study, published in 2008, said about half of all girls and a fourth of all boys reported peer victimization of some kind, including rape, forced oral sex or unwanted kissing and touching.

The acts overwhelmingly took place on school grounds. The study did not specify a time frame for the incidents, and middle schoolers — about one-third of the respondents — were not asked questions about rape or oral sex.