The Great Teacher Effect Debate

Over the weekend and yesterday, there was a small, mini-debate in education circles about teh effect of a great teacher on learning. Eduwonkette noted:

It's everyone's favorite sound bite: good teachers alone can close racial and socioeconomic achievement gaps. But if the entire teacher effect doesn't persist from year-to-year - that is, a student only retains some fraction of the learning advantage they get from having a highly effective teacher - these claims simply don't hold up.

In a new paper, "The Persistence of Teacher-Induced Learning Gains", Brian Jacob, Lars Lefgren, and David Sims estimate how much of the teacher effect fades out over time. It turns out that kids lose more of these short-term test score gains that we (or at least I) thought:

"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."

Yes, you read that correctly. Even if you rely on the upper bound estimates of teacher effect persistance from this study, only a third of that gain sticks around. If you take their point estimate, only 20% of this gain persists. If gains fade out at this rate, we may be overstating the ability of highly effective teachers to contribute to students' long-term academic skills, says Jacob:

"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. Given that a school’s objective is to increase the latter, the importance of teacher value-added measures as currently estimated may be substantially less than the teacher value-added literature indicates." (links in original omitted)

Chad Aldeman of the Quick and the Ed, responded, noting that Eduwonkette got it wrong:

Eduwonkette repeats its finding that, "only about one-fifth of the test score gain from a high value-added teacher remains after a single year." If we dig a little deeper, we see that the researchers found a one-year long-term learning coefficient of .66, with the teacher the student had a year beforehand contributing a full one-third of this effect.

If we look two years out--that is, the student had been under the tutelage of two different educators for two additional years of schooling--that original teacher still contributed about one-fourth of the student's long-term learning gains. These gains attributable to teachers come after controlling for incoming student achievement scores, gender, race, age, income, and learner characteristics (disability and limited English proficiency). These findings in no way challenge previous studies indicating teacher effects accumulate over time.

My wife and I happened to be discussing this concept of the "good teacher" effect over time in a slightly different context.

My eldest daugher had a pretty good teacher this past year and really liked that teacher. The Peanut is concerned that she will not like her teacher so much next year and my wife and I were worries that the teacher next year won't be of the same quality of the Peanut's teacher this year. Would the exceptional gains my daughter made this year be dismantled by a poorer teacher next year?

I began wondering, at least it the context of elementary school, what is the value of the school essentially requiring students have a new teacher every year? I understand that in middle and high school where there is a great deal of subject matter knowledge that is required to be a good teacher in the upper grades makes class changes necessary so that no student will generally have the same teacher in high school for more than say two years in a limited area, such as teh same biology and AP biology teacher.

But at the elementary level, why can't a student have the same teacher for say K-2 and another teacher for 3-5? With the movement of kids for "specials" like art, music, P.E., etc., is not having the same general teacher advantageous? Yes there would have to be accomodations for new student arrivals, movement of children from one class to another for a variety of reasons, including parental problems, but is not there a benefit to be had for the student and the teacher to having the same general classroom make up for two or three years? If the initial learning years are so important, why not maximize the teacher's familiarity with students, their intellectual, physical and emotional development and the opportunity for that student to get the most out of their relationship with a teacher?

Put another way, what is the benefit of changing teachers each year?

Surely I am not teh first person to come up with this concept and question the motivation behind our current "change teachers every year" model? Can anyone give me a solid reason why the current model is superior to a longer term exposure to one teacher?