To 'coolascucumber' and others who said TA's talking to students they support was a problem. I have a TA who has to literally talk her our student through everything that is happening as her disability requires it. I have a stock rule though. I always say, 'The only voice I want to hear while I am talking is Mrs So and so speaking to X. Absolute quiet otherwise please. ' Then the students know that indiscriminate chatting because of Mrs So and so's murmur is not going to be allowed. Alternatively if a TA is nattering just because they want to,I tend to glare around the classroom and ask crossly 'WHO is talking? ' The TA generally then grinds to a halt sheepishly. Hope this helps!