"The nicest thing was the reception the girls gave me," she says. "The other nice thing is the letters you get from all sorts of people. People I hadn't heard of for 50 years: the hairdresser who cut off my auburn curls at the age of 10; the maid we had when we were children. All your relations and fellow heads. A lot of people who wouldn't have dreamt of working in a comprehensive themselves, nevertheless wrote very generous letters."
Mary Green became a Dame Commander of the British Empire in the New Year of 1968. The honour, which came in a list drawn up by Harold Wilson's first Labour government, was an important gesture for state schools in general and emergent comprehensives in particular. Previous teaching dames hailed from a better class of institution - Roedean and North London Collegiate, for example. Dame Mary was head of the 2,000-girl Kidbrooke School in south-east London, the first purpose-built comprehensive in the capital.
Dame Mary had been on a string of grand sounding boards and committees, but the honour, she says, was primarily for her teaching job at Kidbrooke. "As with most headteachers who have an honour of any kind, it's primarily for the school. If I hadn't been at Kidbrooke it wouldn't have mattered how many committees or governing bodies I had served on.
"You always get people who say I can't think why so and so were chosen. It's very chancy - you have to be in the right place at the right time."
Whether she would get an award under today's Labour administration is a different matter. While she shares the government's view that much is wrong with British schools, she also promotes an off-message scepticism about targets and tests. Dame Mary prefers an old-fashioned solution: money for clapped out classrooms, and lots of it.
"When Kidbrooke was built, the money was available to do a very good job. Over the past 10 years schools seem to have become very much the Cinderellas. Now heads manage their own budgets they often have the difficult choice - 'shall I have the outside of the school painted or shall I have another member of staff'."
Working conditions have deteriorated - a factor in the rush for early retirement. And class sizes need to come down for all ages.
"The other thing that the government is doing is introducing endless questionnaires and endless tests. All this statistical work is taking teachers' time away from the major job of teaching."
The whole school, she says, was delighted with her honour, which she acknowledges was a corporate effort. The only minor hazard of damehood has been the title itself. "I have spent 30 years trying to get people to use the term properly. A number of people -banks, building societies - start their letters 'Dear Dame Green'. I tell them but it doesn't make any difference."