Teachers in high-poverty schools in Florida and North Carolina are on average only slightly less effective than those in low-poverty schools. However, within schools, there's a broader talent spread in high-poverty schools, and the poorest-performing teachers in such schools are are generally worse than the least-effective ones in low-poverty schools, according to a new analysis from the National Center for Analysis of Longitudinal Data in Education Research, or CALDER.

What's more, such differences in effectiveness seem to be exacerbated by how things like teacher experience play out in the different types of schools. For example, additional years of teaching experience seem to improve a teacher's effectiveness in a low-poverty school, but less so in a high-poverty school, the analysis states.

The bottom line of the study, according to the authors: Simply attempting to import teachers with great credentials into high-poverty schools probably won't make a long-term difference. Instead, "measures that induce highly effective teachers to move to high-poverty schools and which promote an environment in which teachers' skills will improve over time are more likely to be successful."

The analysis was conducted by scholars from several institutions: Tim Sass, Jane Hannaway, Zenyu Xu, David Figlio, and Li Feng. All are associated with CALDER, a partnership housed at the Urban Institute. For the study, they analyzed matched student-teacher data from Florida and North Carolina, the only states that have such data over many years. The analysis uses a value-added estimate, which tries to determine the effect of the teacher by screening out the impact of students' past performance, family background, peer performance, and school-level factors that might affect learning.

The researchers used a number of techniques to try to ensure that these estimates are accurate. Among other things, they didn't include classes with fewer than 10 students or more than 40, and they made statistical adjustments to deal with the nonrandom assignment of teachers to classrooms. They also ran the analysis using four different specifications to ensure that the findings held up.

Here are some of the findings:

• Under three of the four comparisons, high-poverty schools had teachers who were on average less effective than lower-poverty ones, but the differences were fairly small. What that means, the author states, is that teacher quality in high-poverty schools probably isn't uniformly worse than in low-poverty schools, as it's often thought to be.

• Before you get excited about that, however, the analysis found that the level of teacher effectiveness was more diverse in high-poverty schools than low-poverty ones, and that the least-effective teachers in high-poverty ones were worse than the ones in low-poverty schools. In sum, that means that, overall, poor kids have a greater chance of getting a really terrible teacher than kids attending more-affluent schools.

• What causes this disparity? The authors found that factors like experience continue to make a difference for teachers in the low-poverty schools past the five-year mark, but not so in the high-poverty ones. In English, that means that a teacher in a high-poverty school hits a wall at some point. The authors postulate that such teachers might not have as much access to working with excellent peers as educators in low-poverty schools, or that exposure to challenging students causes "burn out" after a while.

If you're wondering about practical applications and want to read about some policy initiatives that are trying to get at the question of whether it's possible to encourage effective teachers to transfer to—or stay in—high-poverty schools, read my feature story in Education Week.