Infographic: Study shows the long-term impact of teachers |

Infographic: Study shows the long-term impact of teachers

Study shows the long-term impact of teachers
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I don't think any of us are surprised to find out that teachers matter. That has always been obvious, but what I did find interesting--and even surprising--about the information coming from the study on a teacher's long-term impact on a student conducted by Raj Chetty and John Friedman of Harvard University and Jonah Rockoff of Columbia University is the degree to which teachers matter. (See the executive summary or full presentation video.) Their research shows that having a good teacher benefits a child long after that one school year and that measuring a teacher's "value-add" each year is one useful element in evaluating that teacher's performance.

According to Chetty, Friedman, and Rockoff, a teacher's "value-add" is defined as the average test-score gain for his or her students, adjusted for difference across classrooms in student characteristics (such as their previous scores).

Impact of teachers infographic

These three professors conclude "that great teachers create great value, and that test-score based value-added measures are one useful input into identifying such teachers."

What we'd like to hear from you

  1. What do you think about this research? (It is worthwhile
    to watch the full presentation.)
  2. What should be included in teacher evaluations?
  3. How long should a teacher have to improve an evaluation score?

The graphics in this article were created by  Caroline Madigan.



This was really a fantastic presentation. It is nice to see people thinking about education from an economic perspective like this. Some of the figures were shocking - by replacing a SINGLE "lower 5%" teacher with an average teacher for 1 year, a $330k total earnings raise will be achieved - amazing!

To answer the questions you posed:

1) What do you think about this research?
- I really liked how they really proved that the Value-Added measure is unbiased. It seems that too often people make a "necessary but not sufficient" type of argument without even knowing it.

- There was clearly much more than an hours worth of presentation that he stripped down for this talk. He touched only briefly at the end on how to turn these statistics into a policy recommendation. I found two things quite interesting - first there are current attempts to retain good teachers by incenting them with a $2k bonus after their 3rd year if they stay on. However, he noted that 90% of these teachers would have stayed on anyway, so the majority of the funds are spent motivating teachers who did not need the motivation! The second interesting thing was the "how long do we gather statistics about a teacher before dismissing them for poor performance?" question. He showed that with only 1 or 2 years data, we could likely increase total earnings by about $100k by replacing a single lower 5% teacher with an average teacher. Of course by gathering statistics for longer (about 10 years or so) you can be much more certain that you have truly selected a lower 5% teacher, but the return seems to be only about $10k/yr. The point is that if you wait two years so that you gain $110k instead of $100k, you have forgone the $100k for 1 year only to gain $10k the next year!

2) What should be included in teacher evaluations?
There is a great book "Measuring Up" ( that discusses in great detail how to properly design, administer, and interpret tests (for students) properly. When done correctly, it seems they could be a great source of information about the achievement of the teacher (though it seems they are almost never used correctly...). Others ( are passionate that exams/grading should be abolished entirely.

I think it would be very easy for a trained observer to watch a very short presentation (unannounced of course) by a teacher and conduct short interviews with students and come to a conclusion about the quality of their instruction. However, where do the salaries of these reviewers fit into budgets, etc? (Perhaps from the large long term gains predicted by the presentation!)

3) How long should a teacher have to improve an evaluation score?
According to the presentation, less than 3 years. In my opinion, it is extremely hard if not impossible for a teacher to change their ways. So, if they are evaluated with a unbiased, reliable metric that shows them doing extremely poorly, it seems to me that they should be dismissed almost without any time for improvement at all. Surely no teacher in the bottom 5% does not know that they are at or near the bottom! If you believe this, then they have already proven throughout their tenure that they are unwilling to change :)

Thanks for posting this very interesting piece!

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Tadeo Corradi

Lets make teachers even more obsessed with test scores, there are some questions about "third factors" I would like to ask. But I will only say two things:
Teachers matter because they inspire and encourage.
Evaluating impact using earnings is fine, because all we care about is money? I am more proud of one of my students who is humble or kind than one who kills his way to a high paid job.

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Hmmm... I do not know... I am quite perplexed.
To be honest, I did not watch the video since 42 minutes are too many.
Lots of questions come to my mind
- How did they decide when a "top-level" teacher entered in the system?
- What if a student had a top-level teacher for one year and a bottom-level one for five? Does the effect of the top-level still remain?
- It is a comparison very difficult to do, since everyone has his/her history of experiences. How can you compare the outcome of people that had totally different lives? You should take two students, with similar histories that differ only for the presence of the good teacher. I guess you can try to do some kind of statistical analysis to factor out any third factor, but it seems to me very very delicate a job.
- I agree with Corradi that using income as a measure of success is quite near-sighted.
- Also I am afraid about how this report can be read: you are a good teacher if your students get good grades. Unfortunately, nowadays in many places average student score is taken as a measure of the quality of the teacher without thinking that it is quite easy to give A+ to everyone...

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They were very careful to make sure that the Value Added metric is "unbiased", which means they have accounted for the "totally different lives" problem you mentioned as well as possible.

"I agree with Corradi that using income as a measure of success is quite near-sighted." - they also use several other metrics - watch the presentation :). It actually doesn't go into too much detail about the other metrics, but I'm sure they are discussed in depth in the actual papers related to this work.

You said you are worried about "you are a good teacher if your students get good grades." I'd say one of the whole points of the Value Added metric is that we should not trust grades, but rather look at the long term "adult outcomes" caused by teacher variability.

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