Students who pass a baking course could earn league-table credits for their school, equivalent to five good GCSEs, under proposals being trialled this term.
The Office for Standards in Education has warned ministers that the public could lose faith in league tables if the scheme goes ahead.
Ministers want to boost vocational courses by changing the secondary school performance tables from next year to reflect all achievements of pupils at 15 - not just GCSE and general national vocational qualification results.
But Ofsted has attacked plans to give a City and Guilds progression award in baking the same value as five good GCSEs. Its response to consultation on the proposals says: "We believe much would need to be done to convince the general public that this was a proper equivalence."
And it argues that some other vocational courses "may well risk the public good standing of performance tables more generally".
Defenders of the two-year full-time City and Guilds baking award say that it is no easy option. The level 2 course, usually offered in further education colleges, includes units on hygiene and safety, quality systems and procedures, handling and storage of bakery materials, producing bread, cakes or other goods and an investigation of an aspect of the industry.
Derek Williams, of the Bakery Training Council, said: "The award is aimed at providing somebody with practical skills, a broad range of knowledge and an insight into the sector.
"It is quite a considerable package of development with not just external but internal assessment, practical assignments and research.
"Many FE colleges have said that the progression award is too demanding for people getting on to the course at 16 with hardly any GCSEs. If pupils taking the progression award find it really difficult, that is a measure of the standard of the course."
A new system of awarding points for qualifications is being piloted with 245 representative schools. John Dunford, general secretary of the Secondary Heads Association, said: "At the moment, there is a disincentive for schools because vocational qualifications are not recognised in the tables."
The Government has support from around 70 per cent of respondents to its consultation on the changes.
But Ofsted has also warned that the draft points system drawn up by the Qualifications and Curriculum Authority will disadvantage high achievers.
At present an A* at GCSE is worth eight times as much as a G, but under the draft system an A* will be worth less than four Gs.
The schools piloting the system will have results published later this year that show how their average point score and value-added scores would change if all approved qualifications were taken into account rather than just GCSEs and GNVQs.
At the moment, the tables show the proportion of 15-year-olds gaining five or more GCSEs at grade A* to C or the GNVQ equivalent, and the proportion gaining five or more A* to G grades at GCSEGNVQ. They also show the number taking and the proportion passing some other vocational qualifications.
But making intermediate GNVQs the equivalent of four GCSEs has been controversial. The qualification has become increasingly popular leading to criticisms that schools are using it to boost their league-table position.
Last week The TES revealed that Thomas Telford school in Shropshire had made nearly pound;7 million profit from the sale of its online courses, of which the most popular is a full intermediate GNVQ in information and communications technology. The city technology college passes the proceeds on to other schools.
The QCA's list of point scores is due to be finalised after the pilot project evaluation early next year.
A spokeswoman for the QCA said: "We want to get the system right for teachers and schools. Feedback from Ofsted and others has informed our work."
COMING SOON: SHAKE-UP AT 14
* From next year, students can drop design and technology and a language at 14
* Work-related learning, including work experience, will become statutory
* More vocational courses could be given equal status to academic GCSEs
* Ministers aim to raise the percentage getting five good GCSEs by two points a year
* In the long term, former chief inspector Mike Tomlinson, has proposed a baccalaureate-style diploma to replace vocational qualifications, GCSEs and A-levels