The kids don't understand the concept of a balanced argument. To them, it's a black and white world. Argue for one position, then flip over and argue for the other position, then arbitrarily pick their favourite position to conclude.
Kids, argumentative writing obeys the rules of soccer. Your team's goal is at the other end of the field. You score points when you score at that end. You lose points and enrage your supporters when you score goals at the end you are defending. There is no half-time switch over (in case any smart alec should raise that observation).
Always approach your argument with a single-minded purpose. Your audience needs to see the clash, the conflict and the eventual victory. True balance is in respecting the rules of engagement, and not in attacking both goalposts on the pitch.