Adopt a nearby street, beach or park for regular clean ups and/or tree plantings projects.
Run school functions as Zero Waste events.
Use school newsletter to tell parents about sustainability initiatives that are happening in the school. Or hold open days and workshops for parents so they can take learning home.
Plant more trees on school grounds. You may be able to get these donated by members of the community or a local nursery. Native trees will generally require less maintenance and watering.
Start an environmental group in the school. Check out the enviroschools website for more ideas.