No they didn't allow any Christians or their groups/organizations in the NY public school where my daughter went. But they did have rooms available for Muslims to pray when she was in HS (She is now in her late 30's).   When she was in 4th Grade they removed all Christmas from the public school domain.  No Christmas songs/Carols or even Christmas Concerts, no decorations, no mention of Christmas.   They replaced the Christmas Carols with non-secular songs even Jewish songs were allowed but NOT Christian.  (It was the Jews that complained about the Christmas stuff in the schools back then)  Now the Jews in that town are outnumbered by the Muslims.  I can't imagine how happy they are with Muslim prayer rooms in their Public Schools... but it has been going on there now for years.