San Francisco's oldest, largest co-operative preschool is best known for its policy obliging students' occasional urge to take off their clothes and run around outdoors. This self-consciously libertine reputation emanates from a rigorous educational philosophy designed to make sure children enjoy learning throughout life. To keep daily, unrestrained play from turning into a preschool Lord of the Flies, the school maintains a one-to-five teacher-pupil ratio, with adults helping with toy sharing, movement between activities, helping frustrated or angry kids cool off, and making sure kids' clothes eventually get put back on on the rare occasions kids evoke the nakedness-rights rule. Think of this as the preschool equivalent of the "conference" method of teaching typical in graduate school seminars, where instructors nudge — rather than direct — student inquiry, study, and discussion. If all goes well, tots will enter kindergarten as eager hand-raisers rather than hell-raisers.