A generation ago, schoolchildren caught fighting in the corridors, sassing a teacher or skipping class might have ended up in detention. Today, there’s a good chance they will end up in police custody.

Stephen Perry, now 18 years old, was trying to avoid a water balloon fight in 2013 when he was swept up by police at his Wake County, N.C., high school; he revealed he had a small pocketknife and was charged with weapons possession. Rashe France was a 12-year-old seventh-grader when he was arrested in Southaven, Miss., charged with disturbing the peace on school property after a minor hallway altercation.

In Texas, a student got a misdemeanor ticket for wearing too much perfume. In Wisconsin, a teen was charged with theft after sharing the chicken nuggets from a classmate’s meal—the classmate was on lunch assistance and sharing it meant the teen had violated the law, authorities said. In Florida, a student conducted a science experiment before the authorization of her teacher; when it went awry she received a felony weapons charge.

Over the past 20 years, prompted by changing police tactics and a zero-tolerance attitude toward small crimes, authorities have made more than a quarter of a billion arrests, the Federal Bureau of Investigation estimates. Nearly one out of every three American adults are on file in the FBI’s master criminal database.

This arrest wave, in many ways, starts at school. Concern by parents and school officials over drug use and a spate of shootings prompted a rapid buildup of police officers on campus and led to school administrators referring minor infractions to local authorities. That has turned traditional school discipline, memorialized in Hollywood coming-of-age movies such as “The Breakfast Club,” into something that looks more like the adult criminal-justice system.