I never liked the idea of people being trained in groups. The teamspeak channel idea is quite nice as well.

Back in my day TTT handled trainings 1 on 1 TS spacer and things went well and I believe back then we had the most capable staff we have ever had. It allows the LT to get better touch with new recruits and ensures they know what they do
I have experience of one situation in training multiple people at once and I could feel the quamity of the training go down the drain
In my time we also had designated trainers. Some LT never trained or trained 1 guy every now and then so this policy would only bring good things