When the police arrived at Creekside Elementary School in Milledgeville, Georgia, in 2012, they found Salecia Johnson crying and flailing on the floor of her principal’s office. The principal said she was inconsolable, had thrown various items, and had damaged school property during a tantrum. Salecia was handcuffed and transported to a police station. She was 6 years old.

The arrest enraged her parents and community members, who wondered how an institution of learning could call the police on a kindergartner. But overall, black students of all genders are disproportionately disciplined in school — though they actually do not misbehave more than their peers. Researchers have found that excessive suspensions and expulsions lead to various negative outcomes for students, including dropping out of school — and studies have shown that high school dropouts are more likely to be incarcerated than those who graduate high school.

Over the past 20 years, advocates, students, educators, and researchers have coined the term “school-to-prison pipeline” (STPP) to describe how harsh school disciplinary policies and law enforcement policies intersect to feed young people into the criminal punishment system. This is part of a national trend that criminalizes rather than educates students — and one that disproportionately targets black students — as “tough-on-crime” policy has resulted in millions of mostly black and brown people winding up behind bars. Nationally, since 1990, spending on prisons has increased three times as quickly as spending on education.

Over the past 15 years, black girls have been increasingly subjected to harsh disciplinary policies, including excessive suspensions, expulsions, and arrests that push them out of school. In September, the Black Women’s Justice Institute released a report, based on U.S. Department of Education data from 2013–14, that found black girls were more than six times more likely than white girls to receive an out-of-school suspension. Though black girls made up only 16% of female students in U.S. public schools, they made up 43% of girls who were referred to law enforcement and 38% of those arrested.

The 2015 report “Black Girls Matter: Pushed Out, Overpoliced and Underprotected” presented Department of Education data that showed while black boys were suspended three times more often than white boys for the 2011–12 school year, black girls were suspended six times more than white girls. In other words, black girls were more disproportionately targeted by harsh disciplinary policies than were black boys.

Cops in schools (sometimes called "school resource officers") play a critical role in this pipeline. Since the 1950s, some U.S. schools have had on-site police, and as late as 1975, only one percent of U.S. schools reported having police officers. But by the late 1990s, most urban schools had cops. In fact, New York City public schools currently boast a force of 5,200 school resource officers (including 200 uniformed police officers) — meaning schools in NYC employ more cops than counselors. Many schools also have metal detectors and surveillance cameras under the pretext of keeping students safe.

The presence of police officers in schools often leads to harsher, sometimes brutal treatment of the students within. According to a 2011 report from the Justice Policy Institute, “when schools have law enforcement on site, students are more likely to be arrested by police instead of discipline being handled by school officials. This leads to more kids being funneled into the juvenile justice system, which is both expensive and associated with a host of negative impacts on youth.”

This has been proved again and again. In 2015, video of officer Ben Fields brutally assaulting a black student named Shakara at Spring Valley High School in Columbia, South Carolina, became national news. Fields dragged the 16-year old girl from her chair and threw her across the room, an act filmed by another student, Niya Kenny. Kenny was charged with "disturbing the school," a misdemeanor with a possible penalty of 90 days behind bars or a $1,000 fine; (charges were later dropped). She was also suspended from school for several days. This was a highly publicized incident, but similar interactions between school police and students frequently disrupt young people’s educational experiences.

Criminalizing school behavior is not new, especially not for black students. What’s different today is how many more students are being criminalized, and the current intolerance and punitive attitude in schools can be traced back to a spate of school shootings in the 1990s. For example, in 1999, Eric Harris, 18, and Dylan Klebold, 17, both students at Columbine High School in Colorado, killed 13 people and injured 24 others. The post-Columbine era saw the introduction of federal and state laws instituting zero-tolerance policies, which assign “explicit, predetermined punishments to specific violations of school rules, regardless of the situation or context of the behavior.” At the same time, in the streets, the war on drugs led to more punitive criminal legal responses, such as three strikes and mandatory minimum sentencing.

Why are black girls particularly criminalized? This summer, researchers from Georgetown Law’s Center on Poverty and Inequality confirmed that people often view black girls as less innocent and more adult-like than their white peers. Black girls are also more likely to be seen by adults as unruly, aggressive, and disrespectful. Speaking to U.S. News & World Report in May, other researchers also blamed the fact that many black girls attend schools with fewer resources for their disproportionate targeting by harsh disciplinary policies.

The focus on policing and punishing black girls in the classroom often obscures and overlooks the impacts of abuse and violence in students's lives. Studies have found that incarcerated and criminalized girls are often victims of sexual and physical abuse in their early lives, and this is often neither recognized nor identified by school officials or other adults. This reality has led some to coin the term “sexual abuse–to–prison pipeline.”

The realization that zero-tolerance policies in schools have led to criminalization and incarceration for students of color, and especially black students, has prompted calls for restorative justice and other, less punitive discipline practices. Some advocates say that the best way to prevent future incarceration is to invest on the front end in providing excellent educational opportunities for all. To learn more about the school-to-prison pipeline, visit Suspension Stories. To find ways to get involved in interrupting the pipeline, visit the Dignity in Schools Campaign and join their National Week of Action Against School Pushout, October 21–29.

This story is part of Kids Incarcerated, a Teen Vogue series on youth incarceration in the United States for National Youth Justice Awareness Month.