Do low-income students have the same access to effective teachers as their more affluent peers? A new study from Eric Isenberg and his colleagues at Mathematica Policy Research and the Brookings Institution examines this question and draws a surprising conclusion.

In 26 urban districts, the researchers set out to measure the "effective teaching gap," that is, the discrepancy in students' access to effective teachers depending on their socioeconomic status (SES). Teacher effectiveness was determined entirely by value-added scores.

Applying this framework, if all students had equal access to effective teachers, the effective teaching gap would be zero. The reality wasn't that far off the mark and in contrast with the findings from a fair amount of other research. Many (though not all) of the districts turned out to be providing all students, no matter what their SES, roughly the same access to effective teachers.

To the districts' credit, these results reflected a good deal of work on their part. On average, districts in the study had implemented around five common strategies aimed at promoting the equitable distribution of teachers across schools. They include comprehensive teacher induction, highly selective alternative routes to teaching, targeted use of bonuses, performance pay, and early hiring timelines in high-need schools.

What makes this study so different from others that have pursued similar questions and gotten different results? For one, there were clear methodological differences, particularly when it comes to calculating a teacher's value-added score. Isenberg's study controls for peer effects (a measure of how the characteristics of a class as a whole might affect the performance of any one student); however, many other studies do not incorporate peer effects in value-added measures. In addition, this study focused solely on the distribution of teachers within each district, not between them. It did not attempt to answer the question as to an effective teaching gap between urban districts and the suburban districts that border them.

For a detailed discussion of the conflicting literature related to the effective teaching gap, we recommend this CALDER brief, which describes the debate around peer effects, differences in research conducted across vs. within districts, and other methodological points.