It is a mark of his achievement that even the Educational Institute of Scotland, arch-critic of the allegedly increasing politicisation of the HMI, hands down a generous verdict. "He has been one of the better senior chiefs, " according to Fred Forrester, the union's depute general secretary.
"It is true that the Inspectorate has become politicised during the past few years but I suspect that would have happened anyway and Nisbet Gallacher has resisted the trend better than most might have done. He has been forced to put a progressive educational gloss on the implementation of politically sensitive policies, and that cannot have been easy."
Mr Gallacher bequeathes to Douglas Osler, his successor, one legacy which has earned him much gratitude, the continuation of the Inspectorate. There has been no "MacOfsted" to emulate the Office for Standards in Education south of the border.
The "consummate skill" admired by Judith Gillespie, convener of the Scottish Parent Teacher Council, in which Mr Gallacher combines "a talent for encouraging open and free discussion without ever losing sight of where he wants to get to", undoubtedly played its part. Mrs Gillespie, a member of the Higher Still strategy group, has been able to observe him at close quarters as has fellow member Astrid Ritchie, who chairs the Tory education group. "A cautious and pragmatic man who works with the grain" is Mrs Ritchie's assessment.
Mr Gallacher remains reluctant to be drawn into too much detail on Scotland's escape from the OFSTED treatment. "The view of ministers was that our philosophical approach of continuing inspection but broadening it out into quality assurance, school development planning and school self-evaluation was one that best fitted the Scottish system," he says. It is a comment which exemplifies the "charm, effectiveness and understatement" which Mrs Ritchie notes among his strengths.
Mr Gallacher landed the top job in 1987, a significant year. His appointment was confirmed at virtually the same time as the much more explosive debut of Michael Forsyth as education minister.
That was the start of a roller-coaster period, not least for the Inspectorate. Mr Gallacher prefers to describe it as marking "a sea change in the detail of interest shown in education by government". This pushed education near the top of the agenda, which the retiring chief believes is helpful, but also propelled the Inspectorate into a much more public arena, which he says had its disadvantages as well as advantages.
The Forsyth regime certainly forced the Inspectorate to quicken the pace of reform, embroiling it in fierce controversy: Curriculum and Assessment for the 90s came along in November 1987 and soon became the 5-14 programme.
But the process of public exposure for the Inspectorate had begun much earlier with the publication of HMI reports in 1983. And the placing request legislation was the start of the consumer boom which was so central to much of educational change in the past 10 years and which led to innovations such as the inclusion of lay outsiders on school inspections.
Mr Gallacher therefore had to preside over a culture which he characterises as "driving forward the quality agenda", which meant evaluating performance rather than just describing events. This brought particular discomforts such as national testing, performance indicators and the value-for-money paraphernalia embodied in the HMI audit unit.
But Mr Gallacher insists that he and his colleagues have never been uncomfortable with an agenda that has often seemed dominated by a cost-driven, managerial strategy. "Accountability and getting value for money is something that people have begun very legitimately to ask questions about over the past 10 years. But accountability is about quality as well as cost. Value for money is about value as well as money."
His view is a simple one: if the requirements expected of education have become more demanding, it is because society at large and the world of work in particular have become more sophisticated and complex. "We have moved from a situation where, even post-war, we could survive perfectly happily with a minority who were literate and numerate and the rest hard working, to a situation where you are now unemployable if you are not literate and numerate and preferably a number of other things as well, able to work computers, skilled in modern languages and adaptable in moving from one job to another.
"So the message I take from change in education and the constant striving for improvement in education over the past 10 years is not an indictment of the quality of education 10 years ago. It is simply that education is having to satisfy a wider and harder agenda for more and more young people, and, increasingly, for not so young people as well."
If these pressures have forced Nisbet Gallacher to perform a more daring high-wire act than his predecessors, it has not just been a matter of moving from private to public reporting or from describing to evaluating. There has also been close scrutiny of the rest of the acrobatic repertoire.
He himself admits that one of the "tricky" aspects of the job is knowing how quickly reform can be achieved. The launches and re-launches which have buffeted a number of initiatives, school boards, national testing, the 5-14 curriculum, devolved school management and Higher Still, confirmed the suspicion for many that political ambitions often seemed to triumph over educational realities.
But Mr Gallacher says he looks back with particular pride at having "moved the system very significantly forward along the route from just having a sort of spot check inspection system to having a proper quality assurance system which we fuelled through a quite deliberate set of publications, starting away back with Effective Primary and Secondary Schools. That has been a very major priority over the past 10 years."
HMI reports, he stresses, are not just about "identifying weaknesses and deficiencies, though they will do that where that is the case. But they are about broadcasting good practice as well. So one major strand of Inspectorate activity has been to create higher expectations, to up the ante, and therefore to crank up the quality."
Mr Gallacher says his philosophy has always been that "unless you involve everyone in the education system significantly in worrying about the quality of what their school or college or department does, then you will not maximise improvement".
The 5-14 and Higher Still developments, cunningly some might say, have certainly raided the chalk face to find as many practitioners as possible to flesh out these initiatives, thus creating a great number of stakeholders in the success of the policies. But the charges of top-down reforms persist. For Mr Gallacher, however, Higher Still in particular remains an impressive example of "a democratic process at work, involving a massive consultation exercise in which the major consultative outcomes have been reflected in the development as it has gone along".
Higher Still, of course, remains a major piece of unfinished business which Mr Gallacher hands over to his successor. But he will see out the development phase as chairman of the strategy group whose work should finish by Easter 1997, he hopes.
That leaves four terms before implementation of the reform in August 1998 which, Mr Gallacher suggests, is "reasonable". He does not need much prompting to reveal his passionate commitment to an initiative which he believes offers schools "a rational rather than ad hoc set of tools which will meet the needs of a very large and diverse group of students and therefore make life much easier for the schools themselves. Higher Still offers schools a custom-built solution to a problem they already have."
Mr Gallacher urges secondary schools to re-examine their priorities if they believe such developments are becoming burdensome. "Do schools really need to offer the range of choice they do at present in order to offer breadth? Do option lists need to be as extensive as they are in S3 and S4?"
Nowhere is this proliferation more evident and more damaging, Mr Gallacher declares, than in S1 and S2 where the "standstill curriculum" has been a concern of HMI for some time. Concern has now spread to ministers who have asked the Inspectorate to review the relative merits of mixed-ability classes, setting and streaming - the famous "selection within school not into schools".
But he has now reached the conclusion that the problem is more deep-seated than that. He suggests the 5-14 programme, once implemented, will give greater definition to curriculum and assessment but adds: "Until we look fundamentally at S1 and S2, it will be difficult to get value-for-money from the present system."
The problem is one of fragmentation of pupils' learning as they move from one primary teacher covering the full curriculum to be confronted with up to 12 subjects and 16 teachers. "How are we supposed to teach according to each pupil's ability when there is so little consolidated contact between pupils and teachers?" Mr Gallacher asks.
He is too canny to lay the blame at the doors of principal teachers defending their empires, but he does acknowledge that secondary schools have an outmoded structure of promoted posts which require reform. The problem of the early secondary years, however, is not one for secondary reorganisation alone : the upper primary also needs to move away from reliance on one teacher per class, he believes. "So what I am really saying is that the upper primary requires more specialisation and S1S2 less fragmentation."
Whatever priorities schools should set and demands they have to meet, Nisbet Gallacher leaves acknowledging that teachers now have a harder job than they used to. But he puts this down, not to the educational changes meted out by himself and his colleagues, but to social changes. He notes the negative as well as positive relationships parents have with schools and concedes that parental rights and responsibilities are not yet properly balanced. "Education is not just a servant of society but a manifestation of it as well," he observes.
Nisbet Gallacher will undoubtedly miss a career which has seen him negotiate more blind summits and navigate choppier waters than most. Someone who attracts praise from unions, parents and politicians while pursuing a robust agenda is a rare talent: his previous incarnation as a Kilmarnock mathematician and Scottish international batsman was obviously a help in enabling him to calculate well and field the bowling.
Judith Gillespie for one is an admirer of what must be the ultimate balancing act: "Despite the fact that he lives in an ivory tower, he has his feet firmly on the ground."