Imagine that a public high school student posts an editorial cartoon criticizing efforts to expand the Supreme Court on his Facebook page. The next day, when the student arrives at school, administrators pull him aside. They tell the student that because of his post, his classmates are debating court-packing when they should be studying algebra. The administrators give the student an ultimatum: Delete the Facebook post or face school discipline.

This might seem like a blatant invasion of the student’s First Amendment right to speak out on matters of public concern. Yet, it could be allowed if the Supreme Court rules for a Pennsylvania school district in a case argued this Wednesday called Mahanoy Area School District v. B.L.

The case arose from a typical moment of teenage drama: A rising high school sophomore didn’t make the varsity cheer squad. Out with her friend on a weekend and stressing about this snub, she pulled out her phone and opened Snapchat. That’s when the student, B.L., flipped the bird to the camera, took a selfie, and sent the photo to her Snapchat friends with a caption that included “f— cheer.”

B.L.’s “snap” came to the attention of school officials, and the student was punished with a yearlong ban from the junior varsity squad. But B.L. challenged that school sanction in federal court as a violation of her First Amendment rights. The Philadelphia-based 3rd U.S. Circuit Court of Appeals agreed with the student and vacated the suspension. Now, the school district has appealed to the Supreme Court, asking the court to extend a 50-year-old precedent in a way that would fundamentally alter the amount of control public schools have over student lives.

In Tinker v. Des Moines, the Supreme Court ruled in 1969 that public schools could regulate student speech in school when necessary to avoid “substantially disrupt[ing] the work and discipline of the school.” In practice, this has given public schools significant power to curtail student expression within the school environment. Courts applying Tinker have, for example, upheld bans on wearing shirts in school reading, “Old Glory Flew over legalized slavery for 90 years” and “We Are Not Criminals” (the latter in protest of an immigration bill).

But the Supreme Court has never held that Tinker’s rule also applies to student speech outside the school environment, like B.L.’s snap. And for a good reason. As explained in an amici curiae brief filed by the Pacific Legal Foundation, joined by the Cato Institute and satirist P.J. O’Rourke, the Tinker rule has always been problematic because it effectively establishes a “heckler’s veto” within the school environment, allowing some students to silence the speech of others by insisting that it distracts and offends them.

Extending this regime outside the school environment would drastically chill the expression of students at a time of life when they should be finding their voice. And it would instill fear and hostility in school communities, with students aware that anything they say might be reported back to school authorities by an unsympathetic informant.

Tellingly, even the school district was unwilling to offer an enthusiastic defense of the Tinker standard at oral argument. The school instead painted a rosy and limited view of public schools’ Tinker authority, claiming that it does not reach political speech, that it does not allow a heckler’s veto, and that it only applies when students use “terrorizing” language.

But, unfortunately, that is not how Tinker has actually been applied in practice. As Justice Elena Kagan pointed out, the school district’s arguments depended on “a version of Tinker that the lower courts really have not adopted.”

It is striking that the school district was unwilling to offer a full-throated defense of Tinker as it has been applied. In this or a future case, the Supreme Court should narrow the Tinker rule so that only objectively disruptive speech in the school environment can be punished, to prevent thin-skinned classmates from exercising the heckler’s veto. At the very least, the court should decline to extend Tinker into an ever-present speech code hanging over every moment of student lives. Being trained to live their lives without ever giving offense would be a terrible lesson for students to learn.