In the 2001 kids’ movie “Max Keeble’s Big Move,” the evil principal (played by Larry Miller) announces a new disciplinary policy on the first day of school. “I am upgrading my policy of zero tolerance to one of … subzero tolerance,” he says. It was funny at the time, but full decades into the zero-tolerance experiment, it’s hard to laugh: School discipline is out of control, and subzero tolerance is the reality.

When 14-year-old freshman Ahmed Mohamed was arrested and suspended from his Texas high school this month for making a clock that to some people appeared to be a bomb, the Internet couldn’t believe all those adults could act so unreasonably. But unreasonable has been the official policy of many American schools since the early 1990s. The zero-tolerance task force of the American Psychological Association (APA) defined zero tolerance as “a philosophy or policy that mandates the application of predetermined consequences, most often severe and punitive in nature, that are intended to be applied regardless of the seriousness of behavior, mitigating circumstances or situational context.”

Originally based on the mandatory-minimum provisions of the Anti–Drug Abuse Act of 1986, zero-tolerance policies were supposed to insulate all classrooms from a national increase in violent crime. But the 1990s crime wave subsided regardless of enforcement strategies, and there’s little to no evidence of a causal connection between zero-tolerance (or broken windows, as it’s called outside schools) policies and harm reduction. From 1992 to 2011, the rate of in-school nonfatal crime against students ages 12 to 18 declined from 181 to 49 crimes per 1,000 students, but tolerance still keeps decreasing. Kids at school are safer than ever, unless they’re unlucky enough to attract the attention of campus authorities. Rates of suspension have grown substantially for all students in the past few decades as zero-tolerance took hold, but study after study documents unequal increases for nonwhite students.

Predetermined consequences (like Ahmed’s suspension) were supposed to limit racial discrimination in school discipline, but in its review, the APA task force found the opposite. “Data since 1995 indicate that the application of zero-tolerance policies does not appear to have reduced, and indeed may have exacerbated, [racial] disciplinary disproportionality,” it said. Playing dumb with regard to context turns out not to be a good way to reduce discrimination.

In fact, the APA’s task force was unable to find evidence that zero-tolerance school discipline policies accomplish any of their goals. Suspensions tend to lead to more suspensions. Complying with zero-tolerance costs teachers more time than it saves. And as for academic achievement, per the report’s findings, there is “no support for the assumption that zero tolerance, by removing more disruptive students, creates a school climate more conducive to learning for the remaining students.” The policies also increase school use of police and the juvenile justice system, even for noncriminal infractions. In short, zero tolerance is a massive and total failure.