The first morning of the 2005 school year held more than the typical jitters for Toni Kay Scott. One moment, the seventh-grader, known as T.K., was stepping from her mom's Ford pickup to join friends in front of Redwood Middle School in Napa, Calif. Minutes later, the police officer assigned to watch arriving students was steering her toward the principal's office.
Scott, an impish brunet with a tiny nostril stud, had violated Redwood's dress code. The code aimed to squelch gangs by requiring students to wear only certain clothes and solid colors. Scott could change her outfit and stay at school,...