In case you missed it, eduwonkette offered up an excellent
post last month about the accumulation of value-added teacher effects. She describes a new
NBER Working Paper by Brian Jacob, Lars Lefgren and David Sims which suggests that these effects may not as large as prior research has suggested. Here's why:
"Our estimates suggest that only about one-fifth of the test score gain from a high value-added teacher remains after a single year. Given our standard errors, we can rule out one-year persistence rates above one-third. After two years, about one-eighth of the original gain persists.
Our results indicate that contemporary teacher value-added measures may overstate the ability of teachers, even exceptional ones, to influence the ultimate level of student knowledge since they conflate variation in short-term and long-term knowledge.
Our results suggest some caution should be taken in focusing on such measures of teacher effectiveness. If value-added test score gains do not persist over time, adding up consecutive gains does not correctly account for the benefits of higher value-added teachers."
Interesting. If true, this study doesn't say that teachers don't matter, but perhaps less than some value-added proponents have suggested because students may only retain a fraction of the knowledge gained from having more effective teachers in consecutive years.
In case you missed it, eduwonkette offered up an excellent post last month about the accumulation of value-added teacher effects. She describes a new NBER Working Paper by Brian Jacob, Lars Lefgren and David Sims which suggests that these effects may not as large as prior research has suggested. Here's why:
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