IT'S OPTIMAL TO LEAVE SOME CHILDREN BEHIND. Joanne Jacobs discovers that the Phoenix United School District is seeking a millage increase to pay for small, select high schools to serve students whose parents are moving out of the district or putting their children in private schools. That's one millage increase that just might pass. In yesterday's elections, the millage and school bond referenda tended to go down in flames, which may say more about the voters' tolerance for failure than it does about any tax rebellion. The rewards to people for learning higher-order skills are extremely high, and the practice of providing only some low-order skills in order that less-motivated people might view themselves as schooled is an unsustainable waste of resources.