What change or transformation does David Strorm undergo in The Chrysalids?
I believe that David Strorm goes through two main categories of transformation in The Chyrsalids. One transformation is an emotional, allegiance change. The other is a physical change.
Let's start with the physical change. When the story begins, David Strorm is a ten year old boy. By the time the novel ends, David is sixteen. Additionally, David is in full control of his powers and understands his telepathy for what it is. Physically, David is still himself. He has known about his power for a very long time; however, to Waknuk society, David physically changes from "normal" to "deviant." That change in physical status occurs in chapter 12, because Sally and Katherine were tortured until they confessed to the names of the other telepaths.
David's emotional transformation is more important to the overall plot. The change is large, but it is more constant and steady. The reader gets to experience David's emotional changes with David, because the book is written in first person. Because of that, a reader can see David's gradual change from being a Waknuk society member that blindly accepts their critical "genoism" against genetic differences to a person that is actively leading an escape and fight against his former society. It's not that David's overall personality changes though. He stays strong, loving, and caring throughout the novel. What changes is who he directs those attributes toward. His commitment is no longer to his family and society; his commitment is to his new family -- his telepathic friends.