So how is the Federal Government restricting their free speech?
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 entered into a contract with the school. The school does not want to find itself in breach of contract. Did the contract say anything about speech?