A-levels could be made tougher for every pupil within four years, The TES can reveal.
The Qualifications and Curriculum Authority is investigating introducing compulsory harder questions in A2 papers in all academic subjects from 2008. Previously it had been suggested that such questions would be optional.
One or two extra grades would be introduced above an A to recognise the achievements of top-performing pupils on the new papers, the QCA has said.
The move is a reaction to concerns that universities are struggling to select between candidates with strings of good grades, as the number of As awarded has soared in recent years.
The Government first proposed introducing harder questions in A-level papers last year. But it said these would be optional. Students choosing not to answer them would only be able to score an A at best. Only those attempting the harder questions would be able to get the new top grades.
But the QCA is concerned that universities will not take the higher grades into account when selecting undergraduates if the harder questions are optional. It feels some schools may not prepare pupils to take the optional questions; admissions tutors who are unwilling to discriminate against any pupil would therefore only consider the compulsory elements.
Now, in a letter to Ruth Kelly, the Education Secretary, the QCA has revealed it has other fears about the optional questions plan. It worries that only a few students may attempt the harder questions; and it is concerned that those who do should not be penalised if they then do worse on compulsory questions than those who play safe and only answer the latter.
As a result, the authority is to trial A-levels with compulsory harder questions alongside a system where they would be optional.
The letter, from Mary Curnock Cook, QCA director of qualifications and skills, said the compulsory-question model could be simpler to administer, be clear to all candidates and be adaptable to all subjects.
The letter also reveals that an extended cross-curricular project, which is set to be introduced from 2008 alongside A-levels, could also be made compulsory.
As the TES disclosed last week, pupils could gain the equivalent an AS-level by producing, for example, a work of art, a show or a dissertation. Pupils could be required to complete their projects by the end of the autumn term in Year 13, so universities could use them in selection decisions.
The letter said that, if the projects were optional, universities might ignore them for the same reason they would ignore voluntary harder A-level questions. Exam boards will pilot the extended project from September.