New Harvard study about impact of teachers

8 Jan

The Guide to Teacher Quality lists several key attributes of a quality teacher:


Experience is very important. The ability of a new teacher to support student learning

increases greatly during his/her first year of teaching and continues to grow through at least the

first several years of teaching (Clotfelter, Ladd & Vigdor, 2007; Clotfelter, Ladd & Vigdor, 2004;

Hanushek et al., 1998).

Teacher attrition matters. Districts and schools with relatively high rates of teacher

attrition are likely to have more inexperienced teachers and, as a result, instructional quality

and student learning suffer (Alliance for Quality Teaching, 2008).

Ability matters. Teachers with higher scores on college admission or licensure tests as well

as those from colleges with more selective admission practices are better able to support student

learning (Gitomer, 2007; Rice, 2003; Wayne and Youngs, 2003; Reichardt, 2001; Ferguson

& Ladd, 1996; Greenwald, Hedges & Laine, 1996).

Teachers’ subject matter knowledge helps students learn. Students learn when their

teacher knows the subject, particularly in secondary science and mathematics (Floden &

Meniketti, 2006; Rice, 2003; Wayne and Youngs, 2003; Reichardt, 2001).

Preparation and training in how to teach makes a difference. Knowing how to teach

improves student learning, particularly when a teacher is in his/her first years of teaching (Rice,

2003; Allen, 2003; Boyd, Grossman, Lankford, Loeb & Wyckoff, 2005).

Teacher diversity may also be important. There is emerging evidence that students learn

better from teachers of similar racial and ethnic background (Dee, 2004; Dee, 2001; Hanushek

et al. 1998).

One of the important attributes is the subject matter knowledge of the teacher. These findings are particularly important in light of the study, The Long-Term Impacts of Teachers: TeacherValue-Added and Student Outcomes in Adulthood by Raj Chetty, Harvard University and NBER , John N. Friedman, Harvard University and NBER, and Jonah E. Rockoff, Columbia University and NBER .

Here is a portion of the executive summary:

Many policy makers advocate increasing the quality of teaching, but there is considerable debate about the best way to measure and improve teacher quality. One method is to evaluate teachers based on their impacts on students’ test scores, commonly termed the “value-added” (VA) approach. A teacher’s value-added is defined as the average test-score gain for his or her students, adjusted for differences across classrooms in student characteristics such as prior scores. School districts from Washington D.C. to Los Angeles have begun to use VA to evaluate teachers. Proponents argue that using VA can improve student achievement (e.g. Hanushek 2009), while critics argue that test score gains are poor proxies for a teacher’s true quality (e.g. Baker et al. 2010).

The debate about VA stems from two fundamental questions. First, does VA accurately measure teachers’ impacts on scores or does it unfairly penalize teachers who may systematically be assigned lower achieving students? Second, do high VA teachers improve their students’ long-term outcomes or are they simply better at teaching to the test? Researchers have not reached a consensus about the accuracy and long-term impacts of VA because of data and methodological limitations.

We address these two questions by tracking one million children from a large urban school district from 4th grade to adulthood. We evaluate the accuracy of standard VA measures using several methods, including natural experiments that arise from changes in teaching staff. We find that when a high VA teacher joins a school, test scores rise immediately in the grade taught by that teacher; when a high VA teacher leaves, test scores fall. Test scores change only in the subject taught by that teacher, and the size of the change in scores matches what we predict based on the teacher’s VA. These results establish that VA accurately captures teachers’ impacts on students’ academic achievement and thereby reconcile the conflicting conclusions of Kane and Staiger (2008) and Rothstein (2010). These methods provide a simple yet powerful method to estimate the bias of value-added models in any district; interested readers can download computer code to implement these tests from this link.

In the second part of our study, we analyze whether high VA teachers also improve students’ long-term outcomes. We find that students assigned to higher VA teachers are more successful in many dimensions. They are more likely to attend college, earn higher salaries, live in better neighborhoods, and save more for retirement. They are also less likely to have children as teenagers.

Teachers’ impacts on students are substantial. Replacing a teacher whose true VA is in the bottom 5% with a teacher of average quality would generate lifetime earnings gains worth more than $250,000 for the average classroom. VA estimates are less reliable when they are based on data from a small number of classes. However, even after observing teachers’ impacts on test scores for one year, estimates of VA are reliable enough that such personnel changes would yield large gains on average.

Teachers have large impacts in all the grades we analyze (4 to 8), implying that the returns to education remain large well beyond early childhood. Teachers’ impacts on earnings are also similar in percentage terms for students from low and high income families. As a rough guideline, parents should be willing to pay about 25% of their child’s income at age 28 to switch their child from a below-average (25th percentile) to an above-average (75th percentile) teacher. For example, parents whose children will earn around $40,000 in their late 20s should be willing to pay $10,000 to switch from a below-average to an above-average teacher for one grade, based on the expected increase in their child’s lifetime earnings.

Overall, our study shows that great teachers create great value – perhaps several times their annual salaries – and that test score impacts are helpful in identifying such teachers. However, more work is needed to determine the best way to use VA for policy. For example, using VA in teacher evaluations could induce undesirable responses that make VA a poorer measure of teacher quality, such as teaching to the test or cheating. There will be much to learn about these issues from school districts that start using VA to evaluate teachers. Nevertheless, it is clear that improving the quality of teaching – whether using value-added or other tools – is likely to have large economic and social returns.

See, Annie Lowrey’s New York Times article, Big Study Links Good Teachers to Lasting Gain

Teachers also have some thoughts about effective teaching. Valerie Strauss of the Washington Post has a guest column written by teacher Larry Ferlazzo. In Teachers: What We Need to Do to Fix the Schools


Executive Summary of National Bureau of Economic Research Working Paper No. 17699, December 2011


Raj Chetty, Harvard University and NBER

John N. Friedman, Harvard University and NBER

Jonah E. Rockoff, Columbia University and NBER

Executive Summary

Manuscript (NBER         WP17699)

Presentation Slides


Every child has a right to a good basic education. In order to ensure that every child has a good basic education, there must be a quality teacher in every classroom.


Is it true that the dumbest become teachers?

A Review of the Literature Regarding Teacher’s Subject Matter Knowledge

The Importance of Teacher Disposition

The Guide to Teacher Quality

Teacher Quality

What Comprises High Quality Teacher Education?

Educational Testing Services’ Where We Stand on Teacher Quality

Dr. Wilda says this about that ©


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