In most classes there will be a minority of children who are disruptive. Maybe they are over-excited, have poor social skills, are disengaged, troubled by issues at home or have specific learning needs.
The first thing to realise is that they are children and they are not attacking you. They don't know you - how could it be personal? Be calm, professional and remember that these children are in the minority. Take a look at what the children say and you will see that the key factors are to remain calm, be kind, helpful and offer support.
Never accuse a child or ridicule them, no matter how many buttons they are pressing. Instead, remember the language of choice. E.g. "You can choose to continue disrupting your table and do your work at lunchtime, OR you can do your work now and go to lunch with everyone else..."
Work towards what you want to happen, don't dwell on what has occurred. For example, if a child's behaviour miraculously improves the moment you send for the head teacher, praise the child for the right choices. When the head teacher arrives, explain that you are pleased that he has arrived to see child x making good choices.
As a supply teacher you will not have the luxury of time to build up a trusting relationship with these children, so you will need to rely on short-term techniques to help keep their behaviour in check.
Below are a few techniques I know to work, but feel free to add your own at the bottom of the page.
Of course, you still have the behaviour policy. If nothing you are doing is getting through, and the child is unsettling the rest of the class, work towards removing him from the room. Work through the behaviour policy - warnings, 'time out' in class etc. The familiarity and structure of the policy may work to settle child x, or not. Either way, be fair, transparent and consistent.
When the child returns to your class, strike a deal. Explain that you are making a fresh start, and so should he. Explain that you will need to report it to the class teacher, but that you would really like to report on how he has made better choices when he returned. Welcome him back and explain what the class are doing presently.