Serious infractions are dealt with the police. The police are called
first, then the parents. The principal does not even get a chance to have a
closed door conference. Minor infractions are dealt with in the office, but
the door is never closed, at least every time I am in there. The door closes
when there is at least three people in the room - generally, the parent,
child and the principal.
When I was in college, I was always told to leave the door open when I
was alone with a student. There are just too many lawsuits - many of them
false accusations. However, I don't know if this a common practice nor is it
required by any policy/district.