Hi there.
There is a service that you can contact who helps people whose children are in trouble at school. They can give you free legal advice and let you know what you and your son's rights are.

They are called Pan London Education Legal Advice Service (PLELAS)

They are on 020 7247 8998 which is the number for Tower Hamlets Law Centre. Depending on where you are based they will give you an appointment in:
Tower Hamlets Law Centre or
North Kensington Law Centre or
Islington Law Centre or
Greenwich Community Law Centre.

Hope this helps - good luck to you and your son!