I would go further than asking for an assembly. I would demand an assurance that they are implementing a school wide anti-bullying program. Something along the lines of FreindlySchools Plus or similar. If this child is getting away with it then he's probably not the only one. It is disgraceful that they are not protecting the more vulnerable embers of the school community.

Have you had a look at the Bullying No Way site? It might have some links or information that could be useful.
http://bullyingnoway.gov.au/parents/...ied/index.html