I hear you on that, but during a weekend off hours no events, i dont really see the need. As a responsible part 107 holder i understand the validity of wanting to do things with permission. But even if the drone gets lost on school property, technically its public property of the tax payers, at least around these parts, fields and tracks are open to the public to use during off hours, aka there is no posted/private property signs to worry about trespassing to retrieve a lost drone. Again, i totally understand the public safety aspect of this flight during a populated event, during school hours, etc. A school is not a protected area as far as i know. If there is a locked gate somewhere, it would take one call to the building to explain the situation and maybe a day later have your drone back, they cant keep property that doesnt belong to them, even if it did land on their property.
It just takes one overzealous and non educated personnel to respond to your request and say No, without any understanding or possible knowledge of drones, and you are shot down before you even get off the ground, as opposed to being responsible following FAA rules, state, local rules as long as non are preemptive, than doing your flight and possibly being approached by a personal where you get a chance to explain yourself and educate in person if having an encounter at all. If its legal to fly via FAA, State, Local regulations sometimes its better to ask for forgiveness than permission in some instances when in comes to a flight like this in my opinion. A personal interaction can go a much longer way than an email if everything you are doing is legal.
You are even better off letting the police know your flight location/intentions rather than a school board or school official as i have gone this proactive approach when flying in an area, to just let the local PD know where, who and, what i am doing and if they get a call about someone flying a drone they can just say we know. Again vs. a school board official who could just have a power trip and shut you down without knowing any actual UAV laws or regulations, which if you go out and fly anyway since you are legally allowed to do so and then get approached you are putting yourself in a different situation with someone coming out saying "Hey, i told you that you cant fly here" as opposed to "Hey, can i ask you what you are doing?"
Again this is not advocating anything illegal, nor do i think its irresponsible advice, and as long as you follow the rules it should not be any issue to not have to ask for permission. That would almost be like extending that to every building or property you ever flew over no?