England's exams watchdog is looking at whether some GCSEs and A-levels are easier than others.
Is maths harder than business studies?
The Qualifications and Curriculum Authority is to publish a report into claims about the relative difficulty of so-called "soft" and "harder" subjects.
Some universities say candidates who study some A-level subjects are narrowing their chances of a place.
QCA director of regulation Isabel Nisbet said experts had differing opinions about subjects' difficulty.
For example, she said, experts at Durham University placed business studies among the more difficult subjects while Cambridge criticised the course.
Cambridge has said it would not advise pupils to take more than one A-level in a list of 18 subjects, including film studies, social care and sports studies, as part of the three normally needed to obtain a place at the university.
And some academics have argued that subjects traditionally seen as "harder" should be accorded more points for the university application process.
Ms Nisbet said: "If we find differences between the scope of assessment in some subjects, that's something we could look at very quickly.
"We are not in the game of looking at a league table of subjects.
"We won't be trying to suppress debate but we will be trying to shine a light on the debate.
"People need to know when they are starting out on a course of study that it will be respected," she said.
The report could lead to reforms to some exams, the QCA said.
The investigation comes after a government review suggested many teenagers had been steered away from taking languages such as French and German because they were seen as harder than other exams.
The QCA said it hoped to set up a public debate in the autumn about the issue.