I don't know if this counts, but our Lowe's Toolbox project was centered around the idea of being environmentally responsible -- water conservation, recycled plastic fixtures, native plants, solar powered fountain, melaleuca mulch (a giant invasive tree instead of our native threatened cypress), natural pesticides (cedar), organic weed killers, and natural fertilizers/weed barriers (made from corn gluten).
We'll be buying a manual mower, too, to not require fossil fuels in our maintenance at all.
The closest we came to an 'event' was a ladybug release for pest control the week the garden was finished. We gave away grilled hot dogs and gave each kid a cup of ladybugs to spread around the garden.
We also had it certified as a Wildlife Habitat by NWF.
The focus was on butterflies, but it is an ecologically friendly educational garden.
I also had a lot of ideas for earth day revolving around the garden, but no teachers took advantage. Next year, probably.
If I ever escape being president, this will be my main PTO focus, because I think making early connections to the world around us is the way to help children understand environmental responsibility. Too many kids think that the only 'nature' is in the rainforest or the great barrier reef.