I just installed a bogen with talk back system.
the issue i have is that the rooms are noisy and the talk back only works if i cover the mic on the handset,is there a handset that would have a mute button on it for a 2500 type set
thanks

Walker or Sandman.

Or do it yourself by drilling into the handset near the receiver end, on the side, and installing one of these buttons with the NC contacts in series with the transmitter.

When installed properly, it can be pressed with the thumb of the left hand while holding the handset.

How are you going to talk into the handset's transmitter to initiate a page if the transmitter element is shunted? Maybe I'm not understanding your situation completely.

I'm thinking that a Confidencer is more of what you are seeking if I understand you:

HAVE A LOOK HERE

If you are dealing with classroom noise, Ed's suggestion of a confidencer may be just the ticket. A standard 2500 handset has a 'cone' of pickup of about 160 degrees, whereas a confidencer equipped handset has a 'cone' of about 30 degrees.