Special needs children need special needs teachers, those that have extra skills from teachers at regular schools. There will be a degree of extra training involved but there will be plenty of personal quality as well. You will have fewer children to work with but you have to know each child you do have far better than normally. You have to know what to say and how to act with each child throughout the school day, usually without second thought. This applies for everything from a greeting to discipline and all in between.
For some special needs children there can be certain words of phrases that could cause great upset or great favour; getting it right is crucial. So when using discipline for each child you need to know what to accept before discipline is used and what to do when the limit is reached. For example if you have a child with a behaviour problem then discipline for every misdemeanour could mean punishments being dealt out all day. This would waste time and would benefit neither the child or the teacher. You have to base the discipline on the child and the condition the child has.
With an autistic child you have to consider the child and how they react to what is said and done to them. Usual punishment would be based around a form of restriction from doing something. So in the playground to be put against the wall for a period may help, a naughty chair in class is the equivalent. The time in the punishment place can be quite short if the child doesn’t understand time very well, tell them the period and stick to it. Use a sand timer or a countdown clock if available to show what is happening and for how long. Sometimes taking an item from the child may help but with some autistic children a precious item being removed can be more traumatic than is really needed.
One rule for all special needs children is explanation of why they are being punished, even if you know they know what they have done wrong. Ask why, ask what the problem is and explain why you aren’t happy. If the child doesn’t understand then explain as basically as possible, especially if the punishment is because of something that could have happened. For example if they threw something at someone you can explain not only what happened but what could have happened. Above all be consistent and bear in mind who you are dealing with.