Thinking about it... we have had some young geeks here who have found it very hard working at secondary schools, especially their own school.
It's difficult to be staff when you are remembered as a pupil by everyone.
You may find it easier to get started as a volunteer at Primary level. The networks are smaller, but the experience will be no less useful and you'll get an opportunity to learn to be old!
Don't be afraid of contacting the independent schools either