This is a beautifully done video, about the effects doing good things for other people has on our lives. Doing kind things for others doesn't just make them happy. It makes YOU a better person. There is both intrinsic and extrinsic joys to doing things for other people.
Teachers, when you are kind to your students, it matters. Even when they do naughty things, in the long run, you will have an influence on their lives. How will your students remember you?