Really? Did the principal give a sermon? How does reciting the Lord's Prayer indoctrinate Catholics? Your supposing assumes a service, the article doesn't speak of one. The assumption of the priest was that there was an indoctrination purpose. The result, in short, .org over God.
Obviously my example of the Book of Common Prayer passed you by. What the principal did was like a chapel service in accord with Protestant, nondenominational forms. Catholics do not add the doxlogy “for Thine is the Kingdom....” There is an ancient saying: As you pray, so you believe.”