In the case of Tinker v. Des Moines, the protest of the students was deemed protected speech by the Supreme Court. The ruling stated that students do not "shed their constitutional rights to freedom of speech or expression at the schoolhouse gate." This means that, in this particular case, their protest was protected under the First Amendment because it did not substantially disrupt the operation of the school or interfere with the rights of others.
However, if their action had clearly threatened order and safety, it might have been deemed unprotected speech. The First Amendment does not protect speech or actions that present a clear and present danger, incite violence, or pose a direct threat to the safety of individuals or the functioning of an institution.
So, the answer to your question is: "O if their action had clearly threatened order and safety." Under such circumstances, their protest might have been considered unprotected speech.