Mayor Bloomberg is a stalwart supporter of "value-added" scores being released to the public. After all parents need to have this information. The fact that it is thoroughly unreliable, with margins of error so wide you could drive tanks through them is of no importance whatsoever. They need to know!
However, there are also things they don't need to know. For example, they don't need to know how many trailers are being used in Fun City. After all, in 2005 there were 400 of them, and Mayor Bloomberg declared we'd be rid of them by 2012. Now, in 2012, there are 400 of them, and it's fairly clear by any standard just how much value Mayor4Life has added. However, if the city stops releasing information, no one will know about this anymore, and it will no longer be a problem.
The other thing, of course, that no one needs to know, is the status of class sizes. After all, it's kind of embarrassing when you take a billion dollars to reduce class sizes and they just go up year after year. Of course, when you allow ten thousand teachers to retire and fail to replace them, it's more or less inevitable. So once you stop releasing that information, no one knows about it, and the problem is solved.
Now sure, there are those rabble-rousers who complain, oh, the press is sending reporters and camera crews to the homes of teachers with poor ratings, they're being publicly humiliated over the crackpot science you negotiated for them, and they're afraid to leave their homes to go to work. Well, let them get out and become Mayor if they want to change things! Didn't Mayor Bloomberg buy this office fair and square, more than once? Didn't he change the damn law the idiot voters twice affirmed so he could buy it a third time? Let them go out and establish a school board that listens to no one but them, if they're so damn touchy!
The public has a right to know whatever Mayor Bloomberg says they have a right to know! That's how we do things in Mayor Bloomberg's New York!