Made same offer some time ago on the other place, but if you are teaching econ/politics/maths in a state school, and will pay my train/taxi, I will come and do a talk for your kids for free. If you are private I'll do one for a fee donated to a state school/charity.

That's a very generous offer. Hats off to you

Also if you do a talk for a private school insist they invite the state schools they claim to be close to in order to justify their charitable status

May I suggest getting in touch with Speakers For Schools? www.speakersforschools.org