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an hour and 15 minutes, tack two weeks onto the school year, establish universal full-day kindergarten, and rewrite the outdated evaluations used to keep the city’s educators accountable.

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One key issue remained: the autonomy of principals. The question was whether individual principals would have the ability to hire faculty of their own choosing, or whether, as Lewis preferred, principals would have to select from a limited pool maintained downtown with the union’s strong input. Honestly, because I’d gotten everything I really wanted, I was tempted to fold. The reform gospel doesn’t pay much mind to principals. Moreover, the new accountability standards promised to rid the schools of bad teachers.

But while I was preparing to brief reporters assembled at Tarkington Elementary on Chicago’s South Side, Mahalia Ann Hines, a former school principal (who happens to be the artist Common’s mother) pulled me aside. Hines, who holds a doctorate from the University of Illinois, had spent 15 years as a principal, at grade levels from elementary through high school. If we were going to make lasting improvements to Chicago’s schools, she argued, principals needed that flexibility. Without it, they would not be able to establish the right culture or create a team atmosphere. And, at least as important, principals would not have the leverage to coach teachers struggling to help their pupils succeed.

Thinking about it now, years after I decided to abandon the gospel of teacher-focused reform for an approach centered on empowering principals, Hines’s advice sounds almost like common sense. But at the time, it was a momentous decision. Parents are rarely surprised when I note that even the best teachers can be rendered ineffective in a dysfunctional school, or that a great principal can turn a good teacher into an extraordinary educator. But even today, reformers rarely take the impact of principals into account.

The union was loath to give in, and the strike dragged on for two additional days. But eventually they agreed, and I then decided to go all in on principal-centered reform. We raised principals’ salaries, particularly for those working in hard-to-staff schools. Chicago established a new program explicitly designed to recruit and train new school leaders. We collaborated with Northwestern University to improve professional development for principals. And we gave the best-performing principals additional autonomy by establishing a system of independent schools, subject to less oversight from the central office.