It would be unconstitutional for the school or any gov. institution to interfere with voluntary religious activity.
As long as the school, if it is a state school, doesn't endorse religious activity, there is no issue.
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
A man should look for what is, and not for what he thinks should be - Albert Einstein