A couple of weeks ago, a Florida federal judge issue an injunction against an elementary school who wanted to incorporate a religious song into their curriculum. You can read the decision accompanying that injunction
The school district then went and replaced the song with another one "Chatter with the Angels". Its lyrics are less explicit and it was a song sang by slaves, but the same judged suggested that it would be just as unconstitutional to have the children sing it. He didn't rule on the matter because the school had agreed to remove the song, but he said: "This court is also certain that defendants understand what may happen if they continue ... introducing songs that are unconstitutionally religious in nature to public elementary school students"