At our school they get three warnings then they are removed from the situation either by sitting in the corridor to do their work or going to another teacher's classroom.

I think that in a group dynamic they do need an option that removes children because clowns like my DS2 will continue to play to their audience if the teacher can't remove them. I don't see it as punishment so much as allowing the rest of the class to be able to continue to function without disruption. I also think that it's important that children realise that there are consequences for their actions - one day they have to work and offices don't have a naughty corner. It's 3 warnings and then you lose your income.
All of the above.

At our private (catholic) school there has been the 123 - time out "discipline/punishment" in place since kindy. Currently my DD is in Yr 3 and they still do it. My mum teaches at another local catholic primary and they also have the same system. I don't see it as a bad thing at all.

Teachers cannot teach if a child is continually disrupting the classroom and it is unfair on the other children to put up with it. And unfortunately the reality is with large class sizes that a teacher cannot afford to sit down and spend a lot of time focussing on the individual who is being disruptive and spending lengths of time explaining to them what they did wrong...what is the rest of the class meant to do while this occurs? Kids need to learn that in certain situations there are rules or expectations of behaviour and if they "break" these that there is going to be a consequence. As an adult you also have consequences to your actions/behaviours.

I say leave the teachers and the discipline alone personally and leave the teachers to teach.