As some of the previous answers have suggested you MUST contact the board of governors. I sit on the board of my childrens' school and can assure you that they will have to take your concerns very seriously. This is a child protection issue and not only should there be a designated child protection teacher, but there is a designated child protection governor, both of whom are trained in the area. Document every incident, express your concerns as to the seriousness of some of your sons injuries and if (god forbid) another incident occurs, you could seek medical attention to have concrete evidence of any physical harm. Not only does your son need protecting but so does the child who is hurting your him and constantly excluding him is obviously not working. Good luck and keep us posted x