4. Reasoning of the Court

Justice Abe Fortas wrote for the majority. He first emphasized that students have First Amendment rights: “it can hardly be argued that either students or teachers shed their constitutional rights to freedom of speech or expression at the schoolhouse gate.” While schools certainly have the right to establish rules relating to: “the length of skirts or the type of clothing, to hair style … or aggressive, disruptive action or even group demonstrations.” This case does not involve any of those issues. “The school officials banned and sought to punish petitioners for a silent, passive expression of opinion, unaccompanied by any disorder or disturbance on the part of the petitioners. There is no evidence of petitioners’ interference with the schools’ work or of collision with the rights of other students to be secure and to be let alone. Accordingly, this case does not concern speech or action that intrudes upon the work of the schools or the rights of other students.”

He also cited previous cases to further solidify his reasoning:


“In West Virginia v. Barnette, supra, this Court held that under the First Amendment, the student in public school may not be compelled to salute the flag. Speaking through Mr. Justice Jackson, the Court said:
"The Fourteenth Amendment, as now applied to the States, protects the citizen against the State itself and all of its creatures--Boards of Education not excepted. These have, of course, important, delicate, and highly discretionary functions, but none that they may not perform within the limits of the Bill of Rights. That they are educating the young for citizenship is reason for scrupulous protection of Constitutional freedoms of the individual, if we are not to strangle the free mind at its source and teach youth to discount important principles of our government as mere platitudes." 319 U.S., at 637.”
(http://www.bc.edu/bc_org/avp/cas/comm/free_speech/tinker.html)