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"Volunteering at school"
Tutors and teaching assistants are valued by elementary, middle and high schools. Your school system can probably help you find a volunteer program. You can also be sponsored through a company in your field of expertise. This is especially true in scientific and technical fields.
I know of two websites that have great information for volunteering. The Federal Reitired and Senior Volunteer Program (www.seniorcorps.org) is excellent, offering lots of different volunteering options. Also, for people 55 and over the Experience Corps link on www.civicventures.org is good place to learn about volunteer opportunities at local schools.
Other questions Boomeraters are asking...
I am interested in volunteering at a local school. Do you have to have a teacher's certification? What's the best way to go about it?