Re: "Islam is a perfect religion"
^Yes he can because Islam recognizes all the Prophets, and teaches to be gentle in delivering the message. Islam's core principles are based on the kindness, offering of peace, and showing the right path. It's just a message. While warning of the wrath of God, and with that warning the people that there is a day of Judgement. Whether they pay heed or not, is between them and Allah/God/Creator.
It is unfortunate though that some of the teachers that these kids are supervised by are themselves taught rigid attitude, which results in the students learning the harsh tone. That is not the way of Islam.
If one is to look at what Islam is all about, Prophet Muhammad (pbuh) is the perfect example. He (pbuh) lived Islam.