My initial doubts emerged four days into what turned out to be the first Chicago teachers' strike in three decades. After a series of arduous negotiations with Karen Lewis, the union president, we'd arrived at the basic contours of an agreement. In return for higher salaries, Lewis accepted my demands to extend the school day by an hour and 15 minutes, tack two weeks onto the school year, establish universal full-day kindergarten, and rewrite the outdated evaluations used to keep the city's educators accountable.