I have an 11 month Russian Black Terrier who barks for attention.  He is fine at home, in fact never barks even when the doorbell goes, but at training class will bark the whole time. 

I take him into town  so he can get used to noise and people and his behaviour is good until we stop and talk to anyone, which is quite often as he's so unusual everyone wants to know what breed he is.

As soon as someone talks to us, the barking starts but once we start walking again he is good.

I've tried ignoring it and tried correcting him, but nothing works (apart from giving a treat which I don't like doing as it just makes him worse).

If he was a small dog people wouldn't mind, but as he is so enormous I don't want anyone thinking he's aggressive, which he certainly isn't.  Has anyone managed to cure a dog of this, or is it something he will grow out of in time?

You have to remember that the breed was developed as a guarding breed, and not as a pet (several of those in Russia need two handlers at shows, and the judge is not able to touch them). Have you tried making him 'Sit' when you stop to talk? Dogs find it quite difficult to bark when they're sitting.

try sitting him with your fingers in his collar, holding his face towards your body, very close. It means that all he can see is you, and has nothing to bark "at". Dogs often bark whilst making eye contact with other dogs or people.This position stops it.This method seems to be very successful with barky dogs at our obedience class....good luck!