Then, as now, militant delegates advocated one-day strikes, but the executive, which in those days carried the majority with them, favoured a more cautious approach that involved sending children home in targeted areas.
During the ensuing nine months a phoney war of words was waged, then in the January of 1971 Mrs Clarkson, a Brent primary headteacher, fired the only real shot of the campaign when she refused to accept 14 extra children. She was immediately suspended and her staff walked out in sympathy. Within days she was reinstated and assured that her school would get a mobile classroom - and normal service resumed.
It would be nice to think that the class size action that the three main teacher unions are contemplating will also have a happy ending. But the fact is that education is a more complex business these days. In 1970 a delegation of NUT leaders could muscle into Essex County Hall and extract a promise of 1,000 extra teaching jobs. No chance of that now, following the advent of local management of schools and the virtual end of local spending freedom. But in one other respect, little has changed. As the conference delegates have been finding on their return to school this week, most heads and teachers are very loath to take any steps that will endanger children's education, alienate parents and leave themselves open to legal action by governors or local education authorities.
That does not, however, mean that they do not feel strongly about large classes, particularly in primary schools. Why else would the Association of Teachers and Lecturers, which has only taken strike action once - for one day in 1978 - advise its members not to teach classes of more than 31? It is true that oversized classes are not teachers' only headache. As the conference debates again illustrated, many teachers are experiencing increased discipline problems, and struggling with well-meaning but time-consuming innovations such as the special needs code of practice.
But unfortunately Mrs Shephard sounds disturbingly like her predecessor when she attempts to downgrade the importance of class size. Teachers are aware that the research evidence on the link between class size and pupil performance is conflicting, and that the quality of the teacher is often more important than the quantity of pupils, but they also know that teaching 36 children is far more draining than handling a class of 18 - a fact that may help to account for the 19 per cent increase in the number of teachers who have retired early on health grounds over the past two years.
Mrs Shephard also did herself no favours when she read the National Association of Schoolmasters Union of Women Teachers' conference her list of 15 variables that affect class size - admission policy of school, its popularity, size of age group, nature of the school buildings, popularity of the subject, popularity of the teacher, quality of teaching, nature of the subject, availability of support staff, size of other groups being taught at the same time, non-contact time for heads and other staff, teaching methods, pupils' attendance patterns, school ethos, and management skills of the head and governors. Every item on that list merited a place (although the suggestion that primary heads had too much non-contact time provoked derisory laughter) but it was strange that funding did not rate a mention. Neither, of course, did she recognise the important impact that the Government's parental choice policy has had on popular schools' intake numbers. Well-regarded primaries often find they have to take out-of-area children on the rare occasions when they fail to reach their maximum admission number, and even if they have reached it they invariably have to go on accepting children ad infinitum if young families move into the catchment area (a ploy that middle-class parents increasingly use to get the school of their choice). Many heads complain that the admission appeals process also undermines their attempts to keep numbers as low as possible but that is probably something that they will have to learn to live with.
But these may represent legal quibbles in the context of the present dispute. The education service's main need now is to see teachers, governors, parents and Government talking to each other, rather than locked in a mutually damaging stand-off. There can be no instant solutions - as Ted Short, the then Education Secretary, said back in 1970, class sizes cannot be reduced "by sleight of hand" - but given that schools rolls are expected to go on rising at least till the turn of the century there should be a concerted national effort to arrest and reverse the steady increase in class sizes. The targets that the National Commission on Education set over a year ago: maximum classes of 30 in most primary schools and lower numbers in reception classes and schools catering for disadvantaged children may be unattainable in the foreseeable future, but we should at least be working towards those commendable goals.