Since the child hasn`t done anything that warrants dismissal for aggressive behaviour you may be stuck for the whole month. If you let him go and try to use your clause you run the risk of getting a bad reputation in the sense that while he is annoying a lot of that is more normal than we would like it to be. By aggressive I am assuming you meant actually there was a risk of hurting someone.

Other than letting the mom know you just simply don`t want to do it anymore and hope she goes not much you can do. Your one out is letting her know of the change in your ability to do school drop off and pick up.