The educational achievement of a country’s individuals is a key determinant of economic growth when measured not just in terms of quantity but in a qualitative matter. Therefore, improving educational attainment should be a priority in most countries. Research suggests that, among school-related factors, teachers matter most, and so the answer in improving education, it appears, is linked with teaching quality. Do better teachers positively influence students’ knowledge and future educational decisions?
First of all, assessing teachers’ quality is not straightforward and it is, in fact, very difficult to measure. Despite common perceptions, effective teachers cannot accurately be identified based on where they went to school, whether they have graduated, neither for how long they have been teaching. The best way to weigh teachers’ effectiveness is to look at their on-the-job performance, including what they do in the classroom and by measuring the progress their students make. Furthermore, student’s grades or test scores may reflect a vast host of influences that do not derive from schooling, meaning that teacher quality is not the only factor that affects student achievement neither is just attending school. The student’s own motivations, inherent ability, support from family and peers play crucial roles as well.
It has been, however, a strong effort to isolate the impact of teachers from all other effects on student’s performance. What research constantly shows is that a more effective teacher, while comparing to the average one, “produces students whose level of achievement is at least 0.2 standard deviations higher by the end of the school year”.
In two new working papers, Raj Chetty, John Friedman and Jonah Rockoff deploy statistical expertise to evaluate the value of teaching with an interesting feature on student’s future earnings, using the “value added” method.
They use a large data-set from an urban American school district that covers 20 years of results including teacher assignments and students’ test scores from the 3rd to the 8th grade. The authors calculate the effect each teacher has on students’ performance after adjusting for demography and previous test scores. They argue that previous test scores are a good proxy for the variety of external influences inherent to each student. Moreover, recent test score do a better job in reflecting teacher’s effectiveness and so the authors also control for that. They also question the possibility that good teacher scores reflect the lucky circumstances of their student’s rather than their abilities but the results do not seem to back up this hypothesis.
In their second paper, the authors compare their measure of teacher quality (“value-added”) against students’ earnings as adults, after once again controlling for previous test scores and demography. Expectedly, exposure to better teachers is associated with an increased probability of attending university and, among pupils who go on to university, as well as with higher earnings. The authors estimate that substituting a teacher at the bottom of the value-added spectrum with one of average quality raises the collective lifetime income of each class they teach by $1.4m.
Concluding, improving the quality of the education system through improving teaching brings a higher chance of students’ going to university as well higher expected earnings. Teacher quality can be improved by replacing teachers with better ones, but this process may be slow, and of limited impact. This suggests that future economic prosperity requires improving the quality of the teachers already working in schools, because “good teachers are worth their weight in gold”.
“Valuing Teachers: How Much is a Good Teacher Worth?”, Eric A. Hanushek (2011), Education Next
“Measuring the impacts of teachers I: evaluating bias in teacher value-added estimates”, Raj Chetty, John Friedman, and Jonah Rockoff, NBER working paper 19423, September 2013
“Measuring the impacts of teachers II: teacher value-added and student outcomes in adulthood”, Raj Cheety, John Friedman, and Jonah Rockoff, NBER working paper 19424, September 2013