kickstand

we agreed that i would come back this year and take photos of events for the yearbook

Sounds to me you made an oral contract to provide images for the yearbook. Yes?

So why should they not use the images?

How slow? you can use a very slow shutter speed to create some interesting effects. It's called "dragging the shutter".

Otherwise I'd stick with somewhere between 1/60 and whatever your sync speed is (probably 1/200?).