Firstly you will need to get the agreement of your teachers because they will have to help train pupils to be mediators. You can tell them to look at the teacher part of this website. There is a book your school can buy which has the training mediators need to do in it. Your teacher will find details about this in the teachers section. Each training lesson lasts one hour and there are 6 of them. Everyone in the class can do these because peer mediation teaches us skills which are useful even if we never become actual peer mediators. Then those who want to be mediators can fill out a form.
You will need to think about where and when you can have mediations. Your teacher will probably be able to help with this.
You also need to think about how you can let people know you have peer mediation. You could do role plays in assembly, make posters or put it into your school newsletter.
Anyone who wants to come for mediation could either just come to the mediators who are on duty or they could fill out a form asking for mediation. You need to decide where to keep these forms for example in the class room, in the reception. The people can then be given an appointment time and told where the mediation will take place.