The Importance of Positive Repetition in the Classroom

I think positive reinforcement and creating love for Allah Subh'anaHu Wa Ta-A'la, that's why t'alim is very, very important. Regarding treating children equally, I have three girls with very different personalities and circumstances. I have to deal with them according to what's best for them as an individual. Whilst I still try to be fair regarding general rules, I do struggle with them finding some things unfair. Am I doing wrong?