There is no doubt that some students in schools behave badly and their behaviour causes difficulty for others either because it has a negative effect on the group or because ordinary students find it difficult to study with them.
One solution is to take these students away and teach them on their own. However, if we simply have them removed after one or two warnings, we are limiting their educational opportunities because it seems to me that a school which caters for difficult students is a sort of "prison" whatever name you give it and the people who go there may never recover from the experience. This can then cause problems for the wider society.
Perhaps we need to look at why the disruptive students behave badly before we separate them. Disruptive students may be very intelligent and find the classes boring because the work is too easy. Perhaps these students need extra lessons rather than separate lessons. Or perhaps the teachers are uninspiring and this results in behavioural problems so we need better teachers. On the other hand, most students put up with this situation rather than cause trouble, and some people argue that we have to learn to suffer bad teachers and boring situations and that students who can't learn this lesson need to be taught separately.
So before we condemn the students to a special school, we should look at factors such as the teaching, because once the children have been separated, it is very unlikely that they will be brought back.