I am going to continue to
play devils advocate here. You have a raked
house, so if you
drop anything to be suspended only a
foot or so about the audience then you will obstruct sight lines for the people in the back of the
house. I realize it is for the end of the show, but people will want to see
curtain call and the like.
Also, if you are dropping something to be suspended a
foot or so above the audience, it this when they are seated or standing? Because if people are standing up into this to walk out of the
theatre, that is 1) a fire hazard, and 2) it will probably annoy more people than it entertains. Anything that can impede the flow of people in and/or out of the
theatre is not a good thing. Especially in a school setting where the bulk of your audience is probably parents and grandparents. The last thing you need is someone's grandmother getting tied up branches and falling or whatnot.
The concept is fun and interesting, the thing is you really never want to mess around with the patrons. In this day and age, you barely have to do anything and someone will turn around and slap you with a lawsuit. It is very different when you go to a show like Blue Man and you expect to get covered in goo and toilet paper and who knows what, but most people don't go to the
theatre expecting or wanting things dropped on them and then have to navigate out of the
auditorium.
I would suggest things like covering the ceiling with vines, or getting some green rope light and winding around the walls and ceiling (maybe with the vines) then lighting it up at the end of the show. It is less intrusive, but it will bring the audience into the show.