There is nothing in our Constitution about the “separation of church and state.” This phrase is often wrongly used as shorthand for the Establishment clause found in the first amendment, which states: “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof.” What that plainly states is that the government will not prefer or establish one religion over another or restrict the practice of religion. Many people who use the phrase “separation of church and state” interpret it to mean the opposite, that the Constitution requires a separation of church and state. But that is simply untrue.
Thus, if the government gives money to a group, such as private schools, it cannot discriminate against a particular school just because it is religious. The recent SCOTUS decision in Espinoza v Montana case is a clear confirmation of that important understanding.