Nearly one in four GCSE entries could be awarded at least an A grade in what is expected to be another record year of results, it was predicted today.
Around one in 12 exams could score a coveted A*, an education expert suggested.
The predictions come just days before teenagers in England, Wales and Northern Ireland receive their GCSE results.
Last summer, the pass rate rose for the 23rd year in a row, with 69.1% of entries achieving at least a C grade.
Professor Alan Smithers, of the Centre for Education and Employment Research at Buckingham University. suggested that this could reach 70% this year.
And the proportions of exams earning top grades could rise slightly, he suggested.
"I would say, that on the pattern of previous years, we could expect approaching 8% to get an A*."
He added that the percentage achieving at least an A grade could nudge up to 23%.
In 2010, 22.6% of exams got an A or A*, while 7.5% were awarded an A*.
As pupils anticipate their results, one union leader warned that tinkering with exams and league tables is damaging for students.
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), said: "The pressure on schools and teachers of the league tables has already led to too much teaching focusing on getting pupils through exams.
"The Government's intention to devalue and limit vocational qualifications in future league tables will tie schools' hands and push many young people into qualifications that don't allow them to develop their talents and excel.
"In addition, this year the arbitrary introduction of new GCSE floor targets is pushing schools to concentrate their attention on borderline C/D pupils at the expense of other pupils.
"We need an education system fit for all, not the select few."
Under the Government's new benchmark, all secondary schools should have 35% of pupils gaining at least five C grades at GCSE, including English and maths, and ministers are aiming to raise this to 50% by 2015.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said he expects another good year of results, with an increase in the numbers achieving five A*-Cs including English and maths.
He said young people are facing "an enormously tough time".
"In terms of difficulties, they are facing fears about unemployment, they are aware of cuts, and changes to university arrangements. Finding a way through that to an informed decision is incredibly difficult.
"We want, and need, young people to be staying in education, I hope they are encouraged by the good results I'm sure they will get, and want to stay in education, and that we can reassure them that it's worthwhile."
Professor Smithers also suggested that this year's results could be affected by the Government's introduction of the English Baccalaureate - awarded to pupils who score C or above in English, maths, science, a foreign language and history or geography.
Students receiving their results next week will have been halfway through their two-year courses when this was brought in, he said.
"It's a case of whether any school changed what they were doing mid-stream.
"They may have been offering half courses in history or geography and said to students 'you will have to do the full course"'.