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.