Freedom of Religion in the United States
Technically speaking, the United States doesn't have a requirement for separation of church and state. What it has is a prohibition against the establishment of a religion by the government or restrictions on the free exercise of religion. This is from the first amendment:
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.
There are some people who believe that the first amendment's prohibition of the establishment of a religion or restrictions on the free exercise of religion is the same thing as separation of church and state.
States also have to follow the rule since the 14th amendment has been interpreted to incorporate the Bill of Rights (the first ten amendments, including the first).
Government operated schools may not require students to join a religion to get schooling.
There are some number of religious universities that receive incidental public funds (student grants and loans) that do have an established religion.
Certain religious people feel that secular schools overly restrict the religious faith of religious students. This remains controversial, as both sides believe that their side has the right of it. One side argues that schools are part of the state and so must be separated from the church; the other side argues that the US constitution prohibits restrictions on the free exercise of religion and the establishment of a "secular church".
Schools in the United States do not have school on the Christian holidays (primarily Easter and Christmas). They provide accommodations for holidays of other faiths (i.e. students may ask to excused on other days and won't be considered truant if observing their religion's holidays). Schools have off both the Jewish and Christian sabbaths but not the Muslim sabbath. Part of this may be that the Jews and Christians explicitly regard the sabbath as a day of rest while Muslims don't.