Congress probably won't debate a Bush administration proposal to revamp Head Start until next year, but lawmakers could learn a lot from a study released last week on one of the nation's most comprehensive urban preschool systems. Published in the Journal of the American Medical Association, the study found that early-intervention programs like Head Start help poor kids stay in school and out of jail. Researchers compared 989 children enrolled in the Chicago Parent-Child Center program, very similar to Head Start, with 550 youngsters in less intensive early-childhood programs. Most of the children, born in 1980, came from families with incomes below the poverty level. The study found that 49.7 percent of preschool participants had graduated from high school, compared with 38.5 percent of those enrolled in other programs. Boys benefited more than girls--a significant result, since black males are at high risk of dropping out. Preschool graduates also had a much lower rate of arrests. Upper-middle-class kids in preschool may feel stressed out by too much too soon, but poor kids clearly benefit from the extra edge.