Do you ever think of giving up teaching and working in a supermarket? If so it is worth remembering that shop workers have to implement changes, too. The latest metrication regulations, for example.

The difficulties faced by shop workers have formed part of the recent stream of complaints about metrication and they have my sympathy. Where I disagree with the complaints, however, is when it is implied that these are sudden, sneaky changes brought down without warning on an unsuspecting and unprepared British public. We have been teaching metric measures in earnest for about 20 years and making some use of them for much longer, even if wider attitudes in society at large have taken longer to shift.

Most teachers have a stock of textbooks which are past their sell-by-date - looking through my own collection I found metric units in abundance. A book from the original Fletcher Maths series published in 1971 included a page of work based on a totally metric supermarket. It could have been a Nineties supermarket if it wasn’t for the pictures of the housewives in their funny orange overcoats and the fact that they were selling milk at 8p a litre and cheese at 6p per 100g.

Fletcher Maths was of course suspected of being rather radical. This is not a claim often levelled at the 10-a-day maths books but I found a 1971 version which was fully metric. Some of the metric measures included still haven’t made it into everyday life, such as the distance between British towns being given in kilometres. There was even a very useful example on the last page about how many diamonds you get to a kilogram.

A book of 14 O-level past papers from 1964-67 had both metric and imperial units appearing in every paper. One of my favourite examples was a three-part question from a 1975 paper. The first part is about area measured in square feet and the last is about lines measured in centimetres. Sandwiched in between is a calculation requiring the subtraction of c florins from p half crowns (answer in sixpences).

The 1941 edition of Elementary Practical Mathematics claimed in the introduction to be fully up to date and so it proved. Not surprisingly, imperial units dominated - looking through the trigonometry section I was reassured to find that those ladders so frequently and carelessly left leaning against walls were measured in feet. But, even here, metric measures cropped up. They were lurking in trigonometry and in another section grandly entitled “Calculation of the weight of a body” which featured a brass ball of diameter 10cm.

So it seems the metric system has been taught for some time, but how successful has the teaching been? There are enough test results and research findings to give at least a partial answer. A favourite type of question is the multiple choice kind designed to see whether children have the feel for the size of units and can therefore spot possible answers.

Three such questions were included in Murray Ward’s survey of 10-year-olds carried out in the Seventies. Somewhat ironically, as a test of a feel for metric units, one question concerned the possible height of a pint milk bottle. In this question, 77 per cent of children were able to pick the correct answer from a list containing 2cm, 20cm, 200cm and 2m. There was a lower success rate on an apparently similar question about the height of a table. A similar question popped up again in the tests reported on in the primary and secondary surveys of 1980. About 80 per cent of 11-year-olds and 90 per cent of 15-year-olds answered correctly.

The primary and secondary surveys also considered the important issue of how units are subdivided - 77 per cent of 15-year-olds knew that 1m = 100cm and 50 per cent of 11-year-olds knew that 1kg = 1,000g compared with 40 per cent who knew that 8oz = 12 lb. It seems that even at the end of the Seventies pupils had some feel for the metric system, but it is certainly worth asking whether they have improved in the past 15 years.

Comparisons are notoriously difficult, but some were made in the APU Mathematics monitoring report produced in 1991. This included comparisons between 1982 and 1987 surveys. Measures is an area in which significant improvement had been made by 11-year-olds. The same was true for 15-year-olds in the sub-section of measures entitled units.

But if the metric system has fared well in schools, what has happened outside? I remember one child stepping off the scales and writing his mass in kilograms on a chart then whispering to his friend, “I really weigh 5 stone”.

For years there was a feeling that the metric system was something teachers pretended existed, although inhabitants of the real world knew better. I think this has improved over the years as pupils come across metric measures more often out of school.

I wandered round the “Back to school” displays during the summer to check this out, somewhat to the disgust of my young companion who thinks the phrase should be banned. We found children’s clothes sold by metric height with most shops not giving imperial equivalents. The rulers all used centimetres, though most had inches as well.

My companion cheered up slightly when we embarked on the next task of trying to buy 100g of loose sweets. We did not succeed for, despite the “pick ‘n’ mix” system, the prices were still per quarter. We did discover that it is possible to buy a kilogram bar of chocolate but resisted.

This picture of schools going metric faster than society does not seem to be what was expected. The 1969 Royal Society booklet Metric Units in Primary Schools seemed to be anxious to introduce metric units into schools as that is what children would encounter outside. Yet in this respect, schools have been at the forefront of what will surely come to be seen as rational and helpful social change.

Perhaps credit will be given to teachers for the contribution they have made to internationalising Britain’s economy?

Perhaps not.

Jenny Houssart is a lecturer in mathematics education at Nene College, Northamptonshire