NCPA - National Center for Policy Analysis

Study Links Good Teachers to Lasting Gain

January 12, 2012

Elementary- and middle-school teachers who help raise their students' standardized test scores seem to have a wide-ranging, lasting positive effect on those students' lives beyond academics, according to a new study that tracked 2.5 million students over 20 years by Raj Chetty and John N. Friedman of Harvard University and Jonah E. Rockoff of Columbia University.

The difference between excellent teachers, average teachers and poor teachers had a substantial impact on the income potential of students.

  • All else equal, a student with one excellent teacher for one year between fourth and eighth grade would gain $4,600 in lifetime income.
  • Replacing a poor teacher with an average one would raise a single classroom's lifetime earnings by about $266,000 for each year of teaching.
  • A low value-added teacher in a school for 10 years will result in about $2.5 million in lost income for his/her students, when compared with an average teacher.

While previous studies suggested that the impact of good/bad teachers does not last beyond a three- or four-year period, this study argues that the impacts have significant longevity, manifesting themselves in areas beyond academics and earnings.

  • Students with superior teachers have lower rates of teenage pregnancy.
  • Students are more likely to enroll in college if they received superior teachers in their younger years of education.

The wide-ranging benefits predicted by this study rely upon a new metric for assessing teacher quality and categorizing them into skill groups: the value-added impact.  The researchers analyzed the difference between students' beginning test scores and they scores after a year of instruction, and used these values to assess teachers.

While they acknowledged variation over time, they pointed out that by controlling for crucial variables such as wealth and conducting their study over many years of data, they were able to largely eliminate that source of uncertainty.

Source: Annie Lowrey, "Big Study Links Good Teachers to Lasting Gain," New York Times, January 6, 2012.  Raj Chetty, John N. Friedman and Jonah E. Rockoff, "The Long-Term Impacts of Teachers," Harvard University, December 2011.

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