Back in 2014, Kristina Ulmer’s sister died in a car crash and when she and her parents visited the scene, they searched for something that belonged to her. While looking in her wallet, they found a stack of tip money from waitressing. Kristina kept it, but for years she wasn’t sure what to do with it. Four years later, while teaching ninth grade English, an idea came to her. Her sister always cared about other people, so Kristina turned that money into the “$20 Kindness Challenge.” Each semester, she gives every student twenty dollars and one assignment, do something kind with it. Students buy supplies for kids, donate to causes, and even pool their money to help more people. The project has now inspired hundreds of good deeds, and teachers across the country.