Answer:
The Supreme Court Ruled that you cannot compel speech
Explanation:
There are two cases relevant to this discussion: West Virginia State Board of Education v. Barnette, the Supreme Court decided 6-3 that the First Amendment not only protected free speech, but also confirmed that "compulsory unification of opinion" is unconstitutional.
Secondly, Tinker v. Des Moines Independent Community School District was ruled 7-2 to allow pure speech, and that stepping into a school property does not relinquish one's First Amendment rights. However, if the article of clothing or display is disruptive to the learning environment, it is within the rights of the school to limit free speech.