Duh, this qualifies too. The Illinois state law the district claims gives them the power says that any school shall suspend or expel any student involved in a "public school fraternity, sorority or secret society" (105 ILCS 5/31-3)
Read the law. Note that it talks about students who join, or who solicit others to join an organization. It says nothing about beating the shit out of anybody. So it's a question of association. But wait! The First Amendment defends that too! I hate when I miss obvious details like that...