For what it's worth at this point in the discussion,  my thoughts are that the role of religion has changed so dramatically since France and Britain were battling for supremacy here in Canada.
Part of that early settlement meant Catholicism and Protestantism issues had to be ironed out as well.  And look, it all sorted itself out over a century and a half....   However, religion in most western societies has changed its appearance.   We no longer say prayers in public schools but I believe the Catholic system still offers religious studies to students.       But all that religiosity has gone by the wayside over the decades; look at the dwindling flocks in Christian churches.

All that said, if the school offers prayers or devotional time for Christian worshippers, then it must be matched by allowing Muslim students their time as well on Friday.  

If  other religions are  not acknowledged in a particular  school, then the Muslim students should leave for prayers in their mosques.