She was surprised. She doesn't know the toll that teaching takes these days, even in a well-supported school.
We stand for commitment, high expectations of ourselves and all our students, the fullest sharing of the educational activities that the school and its community can provide.
This means hard work, but none of her teachers jib at that. Watch a single lesson here, come to a concert or to My Fair Lady, join our engineering project day, and you will understand.
But these past few years have been difficult and bruising. Teachers have withstood a barrage of ill-considered, often contradictory change. I lose count of the "initiatives" that we have responded to, of the endless "policies" that we have to put in place, the petty mechanisms of "accountability" and control. Some good has come from them. In particular, we have maintained the improvement curve that began - as it did in many schools - before the tide of legislation hit us. Unfashionably, we concentrate on our disadvantaged children - the ones who don't show up in the middle-class league tables but who, on any rational basis, are at the heart of this country's educational failure. Almost all of our students now stay on successfully, in school or training, past 16.
There has, however, been a price to pay - and you can see it, this term, on the teachers' faces. Part of it is down to the scandal of resources: the relentless upward pressure on class sizes. "That doesn't affect the quality of the teaching," the pundits say. Try telling that to the independent schools with their small classes, or the parents who support them. The truth is that more children mean more work, more time and, in the social and economic context in which schools work, more problems.
Our school values equality, encouragement and pride - pride in our own achievement, in the achievement of other people, in the school itself, in the environment we create. How many teachers working in state comprehensive schools can possibly feel that those values are shared, are even understood, in the world outside? At the school I'm leaving, our funding per pupil runs to just pounds 2,000 a year. Ring up your local independent and ask what it receives from the Government through the assisted places scheme. On average, it is twice that sum. True, we get encouragement from the local community, which values our achievement and our efforts to improve. But there is not much pride out there in what good comprehensive schools can do, have already done, to overcome the waste of human talent that is still built in to our diverse, socially selective system.
"Do you have one last wish?" she asked. Unhappily phrased, but I took her meaning. "Yes," I said. "I'd like all the people who criticise the country's teachers to spend just one day experiencing school with someone just like you. By the way," I asked her, "what are your career intentions?"
"Oh, that's definite," she said. "I'm going to be a teacher." "Good," I said, "I do hope people value you for it."
The author retires tomorrow after 15 years as head of King Edward VI School in Morpeth, Northumberland.