Reforms to the qualifications could benefit male sixth-formers, according to Professor Alan Smithers.
Official figures show that there was only a 0.3 percentage-point gap last year between the proportion of boys’ and girls' A-level entries awarded an A* or an A grade.
Professor Smithers, director of the Centre for Education and Employment Research at Buckingham University, suggested that changes to the qualifications, and in particular the move away from modular courses, could mean that this gap closes further.
He said reforms to A levels in 2000 – which saw a swing towards pupils sitting exams throughout their two-year courses – had benefitted girls. Now that the recent exams overhaul has reversed this trend, boys may find the new system working to their advantage.
“Curriculum 2000 put all the A levels on a modular basis,” Professor Smithers said. “And, in 2002 when the first grades were awarded, girls leaped ahead at A*-C and at A grade.”
At A grade, the gap increased from 0.8 to 2.6 percentage points, and at A*-C from 3.6 to 6.8 percentage points.
"The change over to modular exams brought about a big difference in the relative performance of girls and boys,” Professor Smithers said.
Experts have previously suggested that girls tend to respond to modular courses, as they apply themselves throughout the course, working towards specific modules or coursework, whereas boys are more likely to revise in the weeks before a final exam.
"I think what happened when A levels changed from end-of-course examinations to modular – which led to a big gap opening in favour of girls – suggests that the reversion to end-of-course examinations will lead to a narrowing of the gap," Professor Smithers said.
This year, the first A-level grades will be given in the 13 subjects that have been reformed: art and design, biology, business, chemistry, computer science, economics, English language, English language and literature, English literature, history, physics, psychology and sociology.
The extent to which the gap between girls and boys closes depends on how much impact those 13 subjects have, Professor Smithers said.
Last year, 26 per cent of UK girls' A-level entries scored at least an A grade, compared with 25.7 per cent of UK boys' entries.
In 2011, there was a 1.5 percentage-point gap, with 27.7 per cent of girls' entries awarded A*-A, compared with 26.2 per cent of boys'.
Teenagers across England, Wales and Northern Ireland receive their A-level results next week.