Did you explain that to her? Or did you just punish her for not having the same value system as yourself? Because, on one hand, you're punishing Girl #1 for breaking a school rule - regardless of personal values. She wasn't disrupting class or cheating by using the cell phone. No "moral code" was broken with cell phone use. But, on the other hand, you're punishing a girl who has broken no school rule, based on your "moral value system". That doesn't seem consistent to me and the kids will see that, too. Which is why they said it was "stupid". Kids DO have the same values as adults. They just don't have the same value system as you.