Autumn brings another host of freshmen to their respective universities to grapple with unfamiliar and often deeply challenging ideas. While college campuses have increasingly become fraught fronts in our nation’s totalizing culture war, American parents trust that a high school education has equipped their children with all the civic knowledge required to engage responsibly with a world of new — and sometimes deeply offensive — ideas.

Such trust is unwarranted. College students often seem uncomfortable with, if not hostile to, unorthodox ideas, yet the crisis of free speech does not begin at the university. A 2016 survey of high school teachers and students found that only 45 percent of students agreed that “People should be allowed to say what they want in public, even if it is offensive to others,” and only 43 percent concurred with the statement that “People should be allowed to say what they want on social media, even if it is offensive to others.” A scant majority of teachers would allow these forms of offensive speech.

Such opinions contravene free speech. Americans have a right to say what they please, even if it’s offensive. First Amendment expert Jeffrey Herbst notes that young people appear to have a different understanding of free speech that is essentially “the right to non-offensive speech.” Mr. Herbst thinks elementary and high schools inculcate a respect for diversity understood as “Don’t say things that could hurt others.”

That’s good advice for life, but not for constitutional law. Most people find some political expression objectionable. Recognizing an “offensive speech” exception to the First Amendment would prohibit a lot of valuable speech.

Kids learn from experience as well as from books, and their experiences all too often suggest that order trumps freedom. A half century ago, the Supreme Court recognized that “students do not shed their constitutional rights to freedom of speech or expression at the schoolhouse gate.” The Court ruled that several young Iowans could not be punished by their principal for wearing a black armband to protest the Vietnam War.

But the Court only offered protection to nondisruptive speech, a category that subsequent courts have shrunk to include only the most milquetoast of expressions. Students have faced punishment for wearing clothing celebrating the United States Marine Corps, questioning President George W. Bush’s fitness for office, proclaiming that “Black Lives Matter,” and bearing an image of Old Glory. All were prohibited because printed images or words could provoke disruptive conversations between students.

High schools also have nearly unlimited power to censor student speech that is or appears to be sponsored by the school. School officials can control the output of student newspapers and student election campaign materials. This power is wielded to ensure that student papers and elections are completely free of the sorts of controversies common in their real-world equivalents, grossly limiting the value of these exercises.

School administrators have exercised prior restraint over school newspaper articles concerning student drug use, teen pregnancy and the dismissal of favored teachers. In one particularly egregious case, a student paper was shut down in its entirety for reporting on the death of a student injured in a school wrestling match. Anything that might provoke uncomfortable discussion between students, teachers and parents — or might diminish the school’s reputation — seems fair game for censorship. Student electoral speech faces similarly arbitrary restrictions, appeals to religion — even in jest — are prohibited, and candidates have been barred from running due to extracurricular Facebook posts critical of school administrators.

High schools have a higher purpose than occupying the time of young people and keeping them out of trouble. We require our children to attend school because we expect the experience to cultivate the sorts of values required to be good democratic citizens. We encourage students to publish newspapers and hold elections not because they are enjoyable, but because we believe that these activities will prepare them to publish real newspapers and participate in actual elections. In school, as in life, such lessons can be disruptive to teachers and objectionable to fellow students. Avoiding both disorder and offense has fostered a generation at best indifferent to vital constitutional values.

Students who are taught that they cannot be trusted to express themselves freely as high school seniors are unlikely to drastically change their expectations upon becoming college freshmen. Teenagers told that quietude born of censorship is preferable to uncomfortable debate will not develop the ability to engage responsibly with perspectives they find offensive, and are likely to embrace censorship, the preferred tactic of adults with power over their lives. Those concerned by the state of free speech on college campuses should look to the dismal state of free expression in American high schools, where students are routinely treated to a multiyear lesson in the value of quashing expression.