The idea seems pretty straightforward: we know teachers can have a huge impact so getting the best teachers with the pupils who need them the most, could make education more equal. It’s an idea that I have suggested myself already a couple of times.

But… this new study by Isenberg et al begs to differ as they find that in most schools there is always a kind of mix and changing this mix wouldn’t have to much effect:

Our results show that low-income students have equal or nearly equal access to effective teachers in the great majority of the districts we analyzed. While individual teachers differ substantially in their effectiveness, both high- and low-income students have a mix of the most effective and the least effective teachers. As a result, providing the two groups of students with equally effective teachers—even over a period of 5 years—would not substantially reduce the student achievement gap in most districts. Similarly, the disproportionate number of novice teachers at high-poverty schools contributes almost nothing to the ETG, and, by extension, to the student achievement gap.

Results comparing students in different racial and ethnic groups are similar. Black students have slightly less effective teachers than White students, but there were no statistically significant differences in the effectiveness of their ELA teachers. Similarly, teachers’ average effectiveness did not differ significantly when we compared Hispanic students with White students or ELs with non-ELs

But I also found a possible explanation for the possible results:

As is true of many districts, a higher proportion of novice teachers in high-poverty schools suggests that there could be inequitable access to effective teachers. Across the study districts, 18.3% of the teachers in high-poverty schools (90% or more low-income students) are novices, compared with 8.9% of the teachers in low-poverty schools (60% or fewer low-income students). In addition, novices in the study districts are less effective than veteran teachers, by 0.022 in average teacher value added. However, we find that the presence of more novice teachers in high-poverty schools does not create substantial inequity, for two reasons.

First, the substantial difference between high- and low-poverty schools in the prevalence of novice teachers translates into a smaller difference between high- and low-income students in the likelihood of having a novice teacher. Although there are more low-income students in high-poverty schools than in low-poverty schools, both types of students attend each type of school. When calculated at the student level, the difference between the likelihood of being taught by a novice teacher is modest, with 14% of low-income students and 10% of high-income students taught by novices (Table 5). In other words, 86% of low-income students and 90% of high-income students are taught by veteran teachers.

The researchers also explain why their results may differ from previous studies:

• the value-added model used,
• the grades examined,
• the scope of the analysis (whether teachers are compared with others in a district or in a state),
• and the states or districts included in the analysis.

And we also know from older TALIS-studies that countries and regions can differ a lot in the amount of inexperienced teachers teaching in high poverty schools:

So have I changed my mind or do I need to? A very good question and I need to read more and think more. But that is how science works.

Abstract of the study:

We examine access to effective teachers for low-income students in 26 geographically dispersed school districts over a 5-year period. We measure teacher effectiveness using a value-added model that accounts for measurement error in prior test scores and peer effects. Differences between the average value added of teachers of high- and low-income students are 0.005 standard deviations in English/language arts and 0.004 standard deviations in math. Differences between teachers of Black, Hispanic, and White students are also small. Rearranging teachers to obtain perfect equity would do little to narrow the sizable student achievement gap between low- and high-income students. We also show that a higher proportion of novice teachers in high-poverty schools contributes negligibly to differences in access to effective teachers.