The conference of the Headteachers' Association of Scotland offers a stern test for politicians, as some have found to their cost. The serried ranks in the St Andrews University chemistry lab do not heckle offensively, but they are prone to muttering, and they compete in asking pointed questions cloaked in jokes.
Helen Liddell, about whom the question is not whether she would get a front-bench post in government but whether it would be in her "shadow" brief of education, passed the heads' examination with flying colours.
She had done her homework, which the heads expect. She came across as committed, which made a change from politicians who are not only reading their researchers' words but sound like it. She also made mistakes, which they like because it is part of their trade to point out shortcomings ("A commendable effort, Einstein, but rather weak conceptually", would be their favoured Record of Pupil Achievement).
Mrs Liddell has had a rough ride from the teacher unions since her party's education policy was published. With its animadversions on weaker brethren, it is too anti-teacher for them. Parent organisations are dubious, too, because they do not share her belief that school boards should be stripped down and rebuilt. In other words, members of the anti-Government consensus are not to be counted as automatic allies of Labour.
Headteachers, it might be thought, would be less sympathetic to Labour than their staffroom colleagues. By the nature of their job they are elitist, at least in estimating their own salary worth. But they appeared to agree with Mrs Liddell on more than just her thoughts about incompetent teachers. They heard her make the most modest of claims about what a Labour government could do by way of increasing resources and improving buildings. They did not probe too deeply into what her party's much-repeated claims about consultation and partnership would mean in practice.
They thought her views were born of parenthood rather than intimate knowledge of the classroom. Since there are more parents than teachers among the electorate (and many teachers are also parents), she had a ready response. Whether heads prefer a minister of education who herself stood before a class was left undebated.
Mrs Liddell made a plea for pupil involvement in schools. She was told that she was behind the times. She might have been better not to mention Denmark. Although she cast doubt on features of the Danish system which she has just seen (consulting pre-school pupils, but also leaving them out of doors for their nap unless the temperature drops below -12 degrees Centigrade), she was clearly impressed by the partnership concept which animates their schools. Michael Forsyth once got ideas from Denmark, as did the Howie committee. Heads prefer to do things the Scottish way.
If Mrs Liddell becomes education minister, she will be a forceful advocate of her case. Civil servants will not find a vacuum into which they can drop the "departmental" agenda. But she will need the experience of her officials (and the wider education community) to turn fine-sounding aspirations into action.