Teacher quality in NYC and Boston

Speaking of lousy teachers, I recently spoke with a teacher who taught for six years in a suburban area before coming to NYC and teaching here.  This is what she said:

My suburban school had good teachers, we were paid decently and nearly all had Master's degrees.  In contrast, when I came to New York and attended training and orientation sessions for new teachers, I was in shock at the low caliber of teachers.

When I asked what percentage of teachers in NYC were beyond redemption (I've asked this question of many knowledgable people and never heard an answer below 20%), she replied:

My experience is that 1/3 of the teachers are really good; 1/3 are OK and with good professional development (not the waste-of-time professional development we have now), could become decent; and 1/3 are hopeless and need to be removed as quickly as possible.

The 1/3 guess is interesting because it's EXACTLY the number a Bain & Co. study of Boston teachers came up with -- as the slide I've posted at www.tilsonfunds.com/Personal/Bainstudy.pdf shows, fully 1/3 of Boston public school teachers failed to impart ANY KNOWLEDGE WHATSOEVER over the course of a year!  These are very frightening statistics -- yet NOBODY knows them!