Pupils should be discouraged from taking GCSEs early because it is often harmful to their education, Michael Gove said today.
The Education Secretary warned that the rise in youngsters sitting GCSEs early on is a "damaging trend".
Around a quarter of students took their maths GCSE early in 2010, and a similar proportion entered early for English, according to Department for Education (DfE) research.
For many students, this is "detrimental" to their results, with youngsters scoring lower grades, Mr Gove suggested.
He has written to Ofsted chief inspector Sir Michael Wilshaw, asking him to investigate how early entry can be discouraged.
In the letter Mr Gove says that taking a GCSE early "can be beneficial where it is undertaken as part of a planned programme of accelerated progression through to A-level and beyond".
But he adds this has become "a damaging trend that is harming the interests of many pupils".
The DfE's research shows that in 2007, there were 67,000 early entries in total for English and maths GCSE, with 2% of pupils overall entering early for English and 5% for maths.
But by 2010, 24% of students took English early, along with 27% for maths - a total of 326,000 early entries.
The research also shows that in 2010, 29% of those entering early got at least a B in their maths GCSE, compared with 37% of all entrants.
And 30% of early entrants got at least a B in their English GCSE, compared to 41% of all entrants.
"[This] suggests that candidates who enter early perform worse overall than those who do not, even after re-sits are taken into account," Mr Gove said.
"It seems likely that candidates are being entered before they are ready, and 'banking' a C grade where their performance at Key Stage 2 (seven to 11-year-olds) would suggest that if they had continued to study the subject and taken the GCSE at the end of Year 11 they could have achieved a top grade."
Last summer, one exam board chief said it would be a concern if teachers were entering pupils for exams early due to the pressure of league tables.
Speaking on GCSE results day, Andrew Hall, chief executive of AQA, one of England's biggest exam boards, said: "Our conjecture is that students might be being entered in the winter to see how they get on and then re-sitting it in summer if they don't get the grade their school thinks they should."
He added: "If it's teachers choosing to enter their students early because they're ready to take the exam, I would say that's fine.
"If it's teachers feeling the pressure of league tables and entering students early to see if they get through the hurdle or not, I'm not sure that is fine."
Last summer's GCSE results showed that 120,787 pupils aged 15 or younger took their maths GCSE in 2011, compared to 32,980 taking it at an earlier age in 2006.