Beth Tomlinson challenges a room full of 100 people to imagine her hand is a brain. Her wrist, the brain stem, which controls functions such as breathing and heart rate. Her thumb, the limbic system, which controls emotions and the fight-or-flight response. Her fingers, the cerebral cortex, where thinking and reasoning takes place. A typical learning brain is like a fist, all pieces working together. But for students who experience trauma — anything from divorced parents to sexual abuse to a...