Mahanoy Area School District v B L (2021), was a United States Supreme Court case involving the ability of schools to regulate student speech made off-campus, such as speech made on social media. The case challenged past interpretation of Tinker v Des Moines Independent Community School District and Bethel School District v Fraser, previous Supreme Court decisions related to student speech which may be disruptive to the educational environment, in light of online communications.

The case centered on Brandi Levy, identified as B L in pleadings, a student at Mahanoy Area High School in Mahanoy City, Pennsylvania, who posted an angry, profane Snapchat message from an off-campus location after she failed to make the school's varsity cheerleading squad. Though sent to a private circle of friends and deleted later, the message was shown to school staff, and B L was suspended from cheerleading the next year under the school's policy relating to social media.

B L's parents filed suit on her behalf in the Middle District of Pennsylvania, arguing that the school district had unconstitutionally punished her for speech made completely outside of the school that did not pose a risk of disruption. The District Court held in B L's favor and that the school's policy was beyond its disciplinary reach under Tinker. On appeal to the Third Circuit, a three-judge panel unanimously affirmed this ruling, but the majority opinion stated that Tinker did not extend to any off-campus speech, while a dissenting opinion believed this conclusion was overly broad. The Third Circuit's decision created a circuit split for the Supreme Court to resolve.

The Supreme Court affirmed the Third Circuit's ruling in regard to B L's case in an 8–1 decision in June 2021, though overruled the Third Circuit's opinion related to off-campus speech relative to Tinker. The Court affirmed that through Tinker, schools may have a valid interest to regulate student speech off-campus that is disruptive, but did not define when this regulation can occur, leaving this open for lower courts in future litigation. The Court ruled specifically for B L that the school's interests to prevent disruption under Tinker were not sufficient to overcome her First Amendment rights.