Tradeoffs are a fact of life. Education is no exception.

The premise of a new working paper from the National Bureau of Economic Research is that most efforts to improve teacher quality require additional resources except this: What if districts could significantly improve student outcomes by moving around the teachers they already have?

Using test score data from school districts in Charlotte, Dallas, Denver, Hillsborough (FL), Memphis, and New York City, the researchers developed a model of "optimum" teacher assignments within districts.

The effort was successful. By reassigning about half of all ELA and math students to a different teacher, the researchers asserted that the district could significantly improve student outcomes without any additional money. In math, the effects of these hypothetical reassignments were comparable to removing the lowest-performing 5% of teachers and replacing them with teachers in the top 25% of performance.

The bad news is that the "optimum" teacher assignments as defined in this model weren't so optimal for achieving educational equity. While the model increased overall outcomes for students in the districts, it also increased the gap between the lowest and highest performing students.

That's only because the model didn't target certain students to be advantaged by the teacher reassignments—not that it wouldn't be possible. The purpose of this exercise was only how can this district make the biggest increase in scores? to which the answer was that more advanced students in the hands of the best teachers are going to make the most gains. We propose going back to the drawing board to see what happens when this question is asked and answered: How can we reassign teachers to advance the learning of children most dependent upon great teachers?