No, it's not ok: the lot belongs to the school district, and legally may not be used by others for parking at non-school events. Doing so is technically trespassing--you're on the school's property for an improper purpose--as well as a parking violation. Now, it's certainly possible school officials will let you do this, especially if you talk to them in advance, have a good relation with them, etc.--but if you do this without approval, you're looking at the possibility of guests getting ticketed of worse. The school may be a public/government entity, but it's still their land and parking lot; you have no more right to park there for a non-school event than you would to park in your neighbor's driveway without permission.