A.H.
Think about volunteer projects that you've done in the past that you might be able to do from home with slight changes (maybe they can fax typing projects to you, for instance). If the school has an annual fundraising carnival, craft show, bake sale, etc., can you help make phone calls, organize it, and/or donate crafts or baked goods for it?
It's really going to depend on the school. Some teachers might appreciate help with grading papers, but others can't allow it because of school policies. Some schools really appreciate donations of home-baked treats for classroom parties and special occasions, while others now have to serve only pre-packaged treats.
I would call the school and ask if there is anything they need done that you can do for them from home. Ask the teachers, ask the school secretary, ask the principal. If they can't think of anything, ask them to keep you in mind if something comes up, and repeat the offer every so often so they know that you are still available and serious. If they don't have much for you to do, you might also call the school district office and make the same offer for all the schools in the district.
In addition, if you want something to keep you busy, you can also look into volunteer opportunities for other organizations. You might try www.volunteermatch.org to get some ideas.
HTH!
--A.