Another pediatrician takes it on himself to explain adolescent behavior to parents who know the problems only too well. What they need are some answers, and they won't find them here. Sex, drugs, obesity, rebellion, depression are all organized and summed up in the usual hand-holding manner. Advice? The usual: don't fly off the handle; try to understand the reason for the behavior. One decent idea translated into a next-to-last chapter is a collection of ""famous one liners"" from either side of the generation gap (""Stop treating me like a baby,"" ""We'll see,"" ""You don't understand anything,"" ""I don't have to have a reason . . . I'm your parent""), but without elaboration it, too, falls flat.