Like most physical therapists, I learned in school that W-sitting is bad. Very bad. The worst. When I talk to other physical therapists, even those who don’t treat children, they remember the same thing. In a recent conversation, one colleague recalled the time she came home from PT school in a panic because her then-5-year-old sister was a W-sitter. It is a single, pervasive, clear message taught to physical therapy students everywhere. W-sitting must always be corrected. But why?