Good teacher, bad teacher

August 27, 2011

There’s a movement afoot to blame everything that is wrong in American education on so-called “bad” teachers. The theory goes something like this: student outcomes are determined by teacher quality so bad teachers need to be weeded out of the education system for the sake of our children. A corollary to this theory is that anything and anyone who stands in the way of firing bad teachers is evil incarnate. Which leads to yet another corollary: teachers’ unions are the main source of evil. (Interestingly, the proponents of these theories rarely talk about the other side, i.e., how to attract the very best teachers and pay them whatever they might ask. Somehow we are supposed to believe that the evil in the system reaches down to the very bottom of Hell and must be punished accordingly, while the good in the system is of a rather simple kind that does not merit any great reward.)

Douglas Harris, writing in Science (12 Aug 2011, p. 826), “Value-Added Measures and the Future of Educational Accountability,” takes these theories to task. Some of the revelations he describes include:

  • So-called ‘value-added’ assessments of teacher quality show that two assessments made during the same school year show only weak correlation at best (0.2 to 0.6)
  • There are different ways to measure ‘value-added’ and the correlations between these tools can run as low as 0.27
  • Only 28-50% of teachers who were ranked in the top fifth of teachers in one year were still ranked again in the top fifth in the subsequent year
  • 4-15% of teachers switched from the top fifth of rankings in one year to the bottom fifth in the subsequent year
  • recent randomized trials show that so-called performance pay in which ‘effective’ teachers are rewarded with higher pay actually has relatively little impact on teacher performance

Ultimately Harris concludes, “Until researchers who have demonstrated the theoretical promise of value-added measures also demonstrate its effectiveness in practice, the vacuum of empirical evidence will continue to be filled by idealogy and speculation.” (Emphasis added.)


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