Examinations run by the Cornish Language Board and accredited by Cornwall's local education authority have been officially approved on the advice of the Schools Curriculum and Assessment Authority, which oversees qualifications.
The decision will prompt celebrations among Cornish nationalists campaigning for greater recognition of Cornish identity, prompted by a resurgence in Celtic language and music together with a sense of injustice at poor investment in the county by the English across the Tamar.
But the step has exposed old rifts between scholars and speakers over which version of the language is most authentic. Polite but pointed accusations are flying between those who believe late or modern Cornish, dating from 1504, is the purest form, and exponents of a different version based on medieval texts.
The medievalists insist that their language reflects the vocabulary and grammar of Cornish in its 15th-century golden age, while purists mutter dark allegations of the use of computers by their rivals to standardise spellings and forms.
The Cornish Language Board examinations fall into the medieval camp. The secretary of the board, Wella Brown, said: "Cornish died at the end of the 18th century, so you have to decide whether to revive the corpse of a man in his prime or of somebody in the latter stages of life. The bulk of the revivalists decide the best option is to take the language at its peak in the golden age of the 1400s and revive that."
The 300 or more people studying this version of Cornish in classes around the county each year will speak a "tidied up" language surprisingly similar to their forebears five centuries earlier, Mr Brown contends.
The purists, represented by the Cornish Language Council, have no truck with standardised forms. They stress the three distinct periods of early, medieval and late or "modern" Cornish. Evidence exists of a fisherman speaking the language as late as the 1890s, the council says, and argues that sufficient record remains of the spelling, vocabulary and sound of modern Cornish to reconstruct it with great accuracy.
Richard Gendall, honorary research fellow at the Institute of Cornish Studies and a member of the council, insisted its version represented true historical Cornish. The language board, he claimed, was beginning to lose ground. "They have lost credibility with the universities, it is only a matter of time before they are rumbled."
As the two camps, and some five other bodies claiming to represent true Cornish, continue their scholarly squabbles, the fact remains that committed Cornish speakers remain relatively rare. Last year, fewer than 60 candidates sat the board exams, and 13 were from outside Cornwall, including the Czech Republic, Wales, Germany and the United States.
Jan Gendall, folklorist and member of the language council, admits: "The numbers of people who could sit down and chat in Cornish on any subject from space travel to knights in shining armour are very few. The number who would shout for help in Cornish if they were drowning are even fewer."