I think this is where all the zero tolerance policies come from. If there is any disciplinary decision that is made where there is discretion by an administrator, there is an opportunity for a lawsuit. With zero tolerance, you remove discretion so you avoid lawsuits at the expense of unnecessarily disciplining students.
I am not a lawyer, but I do no think having the policy would in any way protect against a lawsuit. If anything, I would suspect it could make it easier for one to succeed because you could show that no due process was provided when a state actor delivered a non-judicial punishment to a minor.
You throw kid A out of the class for behaviour, but you don't throw kid B out because he is usually OK.
But then kid A's parents get mad - or think they can make some money - and it turns out that kid A is belgian/green skinned/three eyed/an FSM worshipper and you have a lawsuit. Or at least the threat of a lawsuit which can go away with a large enough payment.
Throw out all kids that break any rule and you have been perfectly fair
So the poorest parents in the whole school have a huge incentive to get their kid kicked out of the school for disciplinary problems, especially if they are a minority and can sue for a big settlement. Some people perceive that their most valuable commodity is to be damaged, such that they can sue for it.
In a poorer minority neighborhood near where I used to live I remember reading a report about a super market closing down a few years back -- when times were relatively good. They cited shoplifting and numerous slip and fall lawsuits against them as reasons for shutting.
