I am often asked about the limits of the First Amendment in the context of high schools in Washington state. The rights of high school students in terms of free speech is often much broader than people might suspect. The first case of the U.S. Supreme Court that truly dealt with this issue was Tinker v. Des Moines in 1969. In Tinker, the court ruled that high school students had a right to wear black armbands to protest the Vietnam war. The Supreme Court held that students had a freedom of expression as long as there was not a "substantial disruption" to school activities. In later decisions, courts have held that schools may prohibit students from using vulgar language, endorsing drug use, or using hate speech. Generally, however, schools are only allowed to regulate or limit a students speech when the student is on school grounds. This rule has also been expanded to speech at off-campus school functions. For example in 2007 the U.S. Supreme Court ruled that a school could punish a student for holding a "Bong Hits 4 Jesus" banner on a public sidewalk because the the event was a school-sponsored event and it was during school hours. 
In the more modern era, the distinction between on-campus and off-campus has become blurred because of the prevalence of social media. If a student criticizes school officials from her home on a social media account, can the school discipline the student if the post has a disruptive effect? This is the precise question before the court in the case of Levy v. Mahoney Area School District. In that case, high school student Brandi Levy was angry because she didn't make the varsity cheer team, and posted a story on Snapchat where she said "fuck school, fuck softball, fuck cheer, fuck everything." She was cut from the junior varsity cheer team, and she sued. The case is currently at the U.S. Supreme Court and a decision is expect any day. Her lawyer pointed out that she was not on school grounds at the time. The school argued that because the rules of the sports team required student to act professionally, this was different from general school rules.