Hi everyone, I'm a newbie, lurking a bit (honestly can't remember how I stumbled on here...!), now I'm making my first post. I wish there was a "reply" (to OP) button, not sure if my comment will be attached to hers...something to consider for Mumsnet PTB.
ANYWAY!!! I just want to really stress that we are not "Looking AT the eclipse". Not to insult anyone's intelligence, but many are unaware about WHY we can't look at the Sun, even in eclipse ("What's the problem? It was totally dim!"), even for "only a second."
We had a 60% (ish) eclipse here (Sunny California!) a few years ago and did a pinhole projector (as OP says to) and it was SO neat! The size of the "image" was about 3-5" across, so it was very easy to see what was going on. We actually were standing near a shade tree, so our big white board "screen" showed a hundred images all at once, as the sun shone thru each gap in the leaves. The best thing about the projected image is that you can watch the progression of the event from start to finish, and not harm your eyes. I don't get that excited about much, but watching the eclipse PROJECTED was truly memorable.
Finally (sorry so long; way to make a good first impression, eh?), I think the school SHOULD make this a learning experience. Surely a bunch of parent volunteers could help AND THEN LEAVE so minimal disruption to the day.