The Christian response of loving others and praying does not exclude other actions such as, when justified, putting them in jail or even going to war.
If we were to simply pray and love others and do nothing else, every nation that was largely made up of Christians would be run over and thoroughly abused by other nations. Meanwhile there would be no one in prison because of our obligation to forgive everyone. God made us in His image and that includes acting reasonably and, as best we are able, to do what is just here on earth. In the face of injustice we are not obligated to simply wait for God to sort things out. Our wisdom may be imperfect, but to act as if we have none would be to trade our divine gift for that of animals.
Back to the subject at hand. There may be sizeable number of responses to this teacher which would be considered "Christian." One of those responses is firing the guy, and that's the one, I believe, that does justice to the severity of the act he perpetrated.
Somehow I don't think this principal or teacher will ever try this stunt again. Make them read the New Testament and quiz them on it. Heap hot coals of fire up on his head and the Lord will reward thee. Proverbs 25:22 and Romans 12:20. That teacher and that principal are going to find out that Jesus is more Jewish than any Jew in Israel. That's what they are inwardly afraid of and that's why they have an aversion to the Gospel. Romans 12:21: Be not overcome of evil, but overcome evil with good.