if you have a problem with the school first put it in writing to the headmaster, send it recorded delivery. If the outcome does not satisfy, write to the chair of goveners, via the school, again recorded delivery and attach a copy of the letter you sent to the head. A meeting will take place between you and them. if the outcome does not satisfy, you them complain to the LEA, who will investigate the school. Put everything in writing, they have to follow proceedure. Ask for a copy of their complaints proceedure, they have to provide you with it. You also have a right to the school behavioural policy, and the Anti bullying policy, and your childs full school report.
Whatever is happening, make sure you keep a diary of events, including details of any meetings you may have had, who with, and what was said. Kidscape are really good at advising, have a chat with them.
Actually, the Police investigating the Police, or 'the rubber heel squad' DOES get results, and put fear into the heart! Not a cover up, ever...