In Tinker v. Des Moines, why did the Supreme Court rule in favor of the students who wore armbands?

It represented their First Amendment rights.

Explanation:

The first amendment states "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances." The students weren't hurting anyone, were following school rules, and had no reason to be punished. They were using their First Amendment rights.

The students didn't disrupt the school environment