But his true love has always been school-teaching (his father was a headteacher). And within a year of starting on the path to university teaching, he knew he had made a mistake. "University students don't need teachers in the same way," he says now. "I couldn't see myself becoming the kind of needed teacher I wanted to be." So after a year's study he handed back the rest of the money and went straight off, untrained, to teach at a school.
It was a girls' secondary modern in Leeds, where his wife had already embarked on a PGCE. He taught the only subject he was qualified to teach - English - and loved it. He loved his next job too, at the highly selective Leeds Grammar School for boys. "After that," he says, "I settled by choice and conviction for mixed comprehensives."
That passionate support for comprehensive education was given voice shortly before the last election when Mr Douglas gave the vote of thanks to outgoing Education Secretary Gillian Shephard at SHA's annual conference in Torquay.
She was personally more popular than her policies entitled her to be, he told Mrs Shephard, before savaging her Government's plans for extending selection as "educationally counter-productive, organisationally chaotic and morally dubious".
Mr Douglas's commitment to comprehensive education was also the reason behind the decision of his own school - Branston School and Community College in Lincolnshire - to opt out in 1993, making him the second GM head in succession to be president of the association. Lincolnshire County Council was proposing to extend selection in its schools: Mr Douglas wanted to keep his comprehensive intake.
While he was politically opposed to the introduction of grant-maintained status, he had long championed - and pioneered - local management of schools. So he considers GM status as just another form of self-management, with one or two vital features that he will fight for all schools to have under Labour's proposed structural changes, notably delegation to schools of funds for professional development.
His own professional development has been in management, not education. "When the chance came to do a masters, I was arrogant enough to think my educational values were fixed and I wanted to work out how to implement them in management terms," he says.
The calm, analytical Mr Douglas, known as a good speaker and writer with a dry wit, belongs to the consultative school of management. The weekly senior management meetings at his school regularly last until 9pm. He's not indecisive, say colleagues, just thorough.
Mr Douglas, 48, was a mean athlete in his youth: captain of football, cricket and athletics at his school - King Edward VI, Bury St Edmunds - and a Suffolk county schools athletics champion. But a combination of fast bowling and discus-throwing at university did serious injury to his back. Now he is an avid sports fan, avid gardener, avid reader and avid father of three academically successful children, who all attended comprehensive schools.