There was a time, not so long ago, when Welsh children would get a sharp rap across the knuckles for daring to speak their native tongue in the classroom. But research is only now confirming that the language of the hill farmers and the bards can be an excellent medium for teaching maths.
Korean and Japanese infants are said to find fractions easier because their mother tongues simplify some key concepts. "One fourth", for example, is expressed as "of four parts one". But Welsh mathematical terms can also provide pupils with greater insight than their English equivalents.
The Welsh translate "eighteen", for example, as un deg ag wyth or deunaw, which means "one ten and eight" and "two nines" respectively. And the greater clarity of Welsh has sometimes proved to be a help in GCSE examinations and other national tests taken by both English and Welsh-speaking pupils.
The 1995 key stage 2 maths test, which contained questions referring to a "quadrilateral" and "plan view" was a case in point. Both of these concepts were more intelligible west of Offa's Dyke because the Welsh for quadrilateral is pedrochr, which translates as "foursides". Plan view is expressed as uwcholwg, which is read, more usefully, as "above view".
But as Dylan V Jones of the University of Wales Aberystwyth will tell the BERA conference this weekend, test-setters have also sometimes found that they have unwittingly put the Welsh at a disadvantage. "Making sure that the English and Welsh versions of a test are the same or equivalent is not a simple task, " he says.
Occasionally even a common English word has no Welsh equivalent (almost unbelievably, there was no accurate synonym for "brown" until recently). But, more often, a word proves problematical because it is more common in one language than in the other.
"The Welsh for 'apples', afalau, is a familiar word while the Welsh for 'pears', gellyg, is not," Mr Jones says. "A question involving apples could therefore be preferable to one which refers to pears." The Welsh translations of common English words such as mini-buses (bysiau bach), tray (hambwrdd) and tracing paper (papur dargopio), which all appeared in the 1995 key stage 2 tests, were also less familiar than the English equivalents.
Further complications are created by the regional Welsh dialects, which are less similar than English dialects, with some words having more than one common Welsh equivalent. A question in a Welsh-medium 1994 key stage 3 sample paper put children in north Wales at a slight disadvantage because it included the word for milk that is used in the south, llaeth, rather than their llefrith.
But national curriculum test-setters are now more aware of such problems. An early version of one of the key stage 2 maths questions last year included onions as an option for extra pizza toppings. But as onions are known as nionod in the north and winwns in the south, the test-setters decided to change the menu. Sensibly, everyone was offered extra tomatoes instead.
The Assessment of Bilingual Pupils: Observations from Recent Welsh Experiences, by Dylan V Jones, Department of Education, University of Wales Aberystwyth