Heads warned of legal challenges after ruling on subject clashes
John Dunford, general secretary of the Assocation of School and College Leaders, issued the warning after a 14-year-old won a fight to have her local authority pay for private French lessons.
Since 2004, secondaries have been required to offer pupils the chance to take key stage 4 "entitlement" subjects: modern languages, art and design, humanities, and design and technology.
Kim Snape, a pupil at Worden sports college in Leyland, Lancashire, wanted to take performing arts but was told she would have to drop French because of a timetable clash.
In a letter, Lord Adonis, the schools minister, said that Kim had the right to study subjects in all four "entitlement" categories.
Now Mr Dunford has said that there are further implications for schools.
From 2008, any pupil achieving a level 6 or above in key stage 3 science tests will have the right to study three separate sciences at GCSE. At key stage 3 from next year they will also be entitled to study cookery.
And from 2010, every five- to 16-year-old will have the right to two hours'
PE per week. Within six years, every 14- to 19-year-old will have the right to demand to study any one of the 14 new diplomas in work-related subjects, at one of three levels.
Mr Dunford said the increasing number of entitlements would lead to an "impossible situation" for schools, which could not be expected to offer all subjects to all pupils without a huge increase in staffing costs.
He said: "Some pupils will not all be able to do what they want. But that has always been the case. It's only because ministers have been throwing entitlements around like confetti that problems have been caused."
Margaret Morrissey, of the National Confederation of Parent Teacher Associations, said schools did not have the teachers or the timetable flexibility to meet all the entitlements.
"I cannot see that the Government has thought through all the implications," she said.