Wow! Just think, if you have a TFA teacher, you gain 2.6 extra months in a year of instruction in math! Or so concluded a recent study by Mathematica Policy Research.
But what does this mean?
Gary Rubinstein, himself an alumus of Teach for America, now a math teacher at Stuyvesant High School in New York City, took a closer look at the study and says it does not mean what it claims.
He writes:
The difference between a group scoring in the 27th percentile and the 30th percentile is very small, .07 standard deviations. To give you an idea of how small this is, a 27th percentile on the SAT math section is a score of a 430 while a 30th percentile is a score of 440, which is a difference of one question out of about 60.
So, on a test of 60 questions, the student of a TFA teacher answered one more question correctly than the teacher who was not TFA. How did that get converted to 2.6 months of gain? Read the post.
Diane Ravitch's blog 
Thanks for the clarification Gary. The 2.6 month gain has always been troubling and somewhat laughable. Until TFA came along I guess no one thought to make these mathematical conversions to show gain and achievement. Gosh, look at what I missed as teacher and as a student. Thanks TFA.
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The Mathematica study is well worth a careful look. The biggest issue I have is that the sample sizes are pretty small so I am surprised that the effect sizes are actually significant.
That said, the TFA math teachers had no background in Math! This is a point that Gary should have mentioned. Moreover, the comparison group had significantly more experience as teachers. There are other differences between the groups as well that a more balanced assessment would have at least mentioned..
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