There are several laws that protect both you and your students. I will assume in my amswer that you teach in a general education classroom, and that the student is not one with exceptional needs. I will also assume that the offending parent was lawfully present on campus pursuant to the school site and/or school district policy.

The victim/student likely has a cause of action against the abusing parent for assualt, battery, and infliction of emotional distress. The victim student would have to sue through a guardian ad litem appointed by the court (typically the parent of the student). There is a two-year statute of limitations in California to sue for personal injury that might be tolled (delayed) until the student turns 18. Your other students who oberved the assualt and battery may also have suffered injury if they were in fear of imminent battery or traumatized. Any of these students can have their parent obtain a civil harassment restraining order, depending on the circumstances, especially if the school district refues to provide protection. You may also have the right to obtain a civil harassment restraining order. However, neither you nor the students should have to resort to this if you simply want the parent to stay away..

The California Education Code requires schools to adopt policies to reduce disruption of the classroom. These policies typically cover parent access and require parents to sign in. It also makes it a misdemeanor for a person not to promptly leave school grounds and stay away for seven days upon the request of the site principal or designee. However, the letter of the law states that it does not apply to certain classes of individuals, including parents. Therefore, you should notify your site administrator immediately to invoke the laws and policies that prohibit interruption of the classroom. The law makes it clear that all other laws and local ordinances still apply, and your city and county may have ordinances against the specific behavior or even more generally disruptive behavior.