Universal pre-kindergarten schooling, every progressive's fondest dream, is back in the news. Bill de Blasio, the overwhelming favorite in the New York mayoral race and the likely future head of the nation's largest school system, is pushing universal pre-K as his No. 1 policy proposal. President Obama offered a national version of this idea in his February State of the Union address and has since pushed hard in other settings. Two problems: Such programs would have negligible educational value, and they would be massively expensive.