Jews say a Hebrew version of the Lords prayer. I recited the English version  in public school. I do not recall it being a 'Christian' prayer. We had a large Jewish majority. There was no issue. We also sang God save the Queen. I refused to do so. I proudly sang 'O Canada' and I still do.
Things have changed, we are no longer a white Christian country. There should be no religion at all in public schools.