We know that great teachers can have a tremendous impact. Yet we don't have policies in place to ensure that all children are taught by great teachers.
That's why the mayor pushed for an evaluation system that would help determine who is excelling, who needs help and who may be better off in another profession.
I'm so glad that, for the first time in Chicago, teacher evaluations will at least consider whether students are learning over the course of the year. But I do wish the union hadn't won some key concessions.
Despite the mayor's efforts, the contract wasn't a home run for kids. It still allows teacher seniority to trump teacher effectiveness in some cases when layoffs unfortunately arise.
And under the new evaluation system, less than a third of a teacher's evaluation will be based on an objective look at how much academic progress his or her students are making.
That's not enough. Educator evaluations ought to consider several factors, but the degree to which our children succeed academically must be what we emphasize.
I also think it's a mistake to include a third-party appeals process for poor evaluations. That's not necessary if you have a robust and fair evaluation system, and it will continue to make it overly burdensome and bureaucratic for principals to replace staff failing to meet students' needs.
One of the mayor's proposals, ultimately rejected, was a performance-pay system for teachers like the one in Washington, which offers huge pay increases to effective teachers, making them - deservedly - among the best paid in the country.
The strike advanced the national conversation about education reform but did so at a high price:
Chicago's children lost roughly 18 million collective hours of learning time; moms and dads across the city lost wages, and possibly risked jobs, so they could care for their kids; and some children went without the hot meals they reliably get at school.
It was frustrating to hear Chicago Teachers Union President Karen Lewis say toward the end of the dispute that the strike would continue to see whether there is "anything else they can get."
But at least that was clear evidence that, for union leaders, this strike was never about what was best for kids.
Going forward, I suspect more Democrats will say, as Emanuel and President Barack Obama have, that it makes sense 1) to look at how much children are learning when assessing a teacher's work, 2) to empower parents to help turn around schools that are failing their kids, and 3) that it is right to pay teachers more but to also hold them accountable for results.
I know that opposing unions on some of these policies isn't easy.
But the more unions attack fellow Democrats, casting everyone who challenges their policies as "anti-teacher" or "anti-union," the more they isolate themselves from the broader Democratic Party.
Ours is the party that understands that the greatest equalizing force we have in this country is a high-quality public education system through which people can escape poverty.
Rhee was chancellor of District of Columbia public schools from 2007 to 2010. She is founder and chief executive of StudentsFirst, a national nonprofit education advocacy group based in Sacramento. Her column first appeared in The Washington Post.