There are three basic constitutional principles for educators and students alike to keep in mind when considering walkouts and other student free speech expression and activities.
Student Protests and Walkouts
Public school students have a fundamental right to free speech and expression.
Both students and teachers have First Amendment rights, applied in light of the special characteristics of the school environment. The U.S. Supreme Court has long held that students do not "shed their constitutional rights to freedom of speech or expression at the schoolhouse gate." (Tinker v. Des Moines Schools)
"Viewpoint discrimination" is prohibited.
School officials can't engage in "viewpoint discrimination," that is, punishing students because of their particular point of view. That means that to the extent that being absent from school to join a protest is considered an unexcused absence, such unexcused absences must be treated just like other unexcused absences. The consequences for a student who engages in protest or civil disobedience by missing class to attend a protest must be the same as a student who, say, misses class to go to the mall.
"Material" or "substantial" disruption may be punished.
Schools may punish speech or expression at school only if it has a "material" and "substantial" disruption on school activities or interferes with other students' rights. One example: Decades ago, courts held that it was wrong for a school to categorically punish any student who wore "freedom buttons" to school during the civil rights movement. The school had no evidence that it would actually materially or substantially disrupt school activities. Not all classroom walkouts will have a "material" or "substantial" disruption on school activities.
It's important to note that a school may punish students for missing class to protest, but if it does, it must do so in the same way that it would punish students for any other unexcused absence. So unless a school has evidence that a walkout or other activity would create material and substantial disruption, it would be constitutionally questionable for an educator to preemptively and categorically impose additional punishments for the mere act of walking out of class.
We encourage teachers to plan for any silent classroom walkout so that it does not materially or substantially disrupt their classes. As the decision in another important U.S. Supreme Court case (West Virginia State Board of Education v. Barnette) found, students' free speech rights must be "scrupulously" protected if we are to have any hope of "educating the young for citizenship" not to "discount important principles of our government as mere platitudes."