See what transpires from the meeting on Monday between the parents and presumably the Senco, Head of Year/personal tutor(?). The parents need to prepare a written list of incidents, dates and times and ask what action is being taken against the perpetrators. They need to know what strategies are available to support their son, and also ask to meet the Governor with responsibility for Special needs.
They should arrange a meeting near the beginning of next term to see what action plan has been prepared. Save threats of the Police and Ofsted for next term. Also ask for support for the boy to access strategies for managing social interaction.
All that being said, I do feel sympathy for schools battling bullying, as they are hamstrung by being allowed fewer and fewer sanctions for dealing with out of control feral children. The time taken dealing with these children impinges increasingly on teaching time of senior staff, thus depriving other pupils of their education and just try getting a child suspended, yet alone expelled. Incidentally, there are no conductors on school buses, only drivers.