Teachers have been taking advantage of "way easier" alternative GCSE exams, headteachers have admitted the day before hundreds of thousands of school children receive their results.
Schools that entered pupils into the International GCSE (IGCSE) knew students were "going to get higher grades than in GCSE", the Association of School and College Leaders (ASCL) has said.
Compared to the standard GCSE exams, the IGCSE - originally established for overseas pupils - is "an absolute doddle", teachers posting in an online forum claimed, according to the Times Educational Supplement (TES).
The annual report by the newspaper revealed that another teacher even admitted the "easy" exams had a "very formulaic approach to answering the questions."
Brian Lightman, general secretary of ASCL, told news.tes.co.uk: "What schools are saying is that it [IGCSE] is easier, there is more flexibility over which books pupils can read and so on, and those schools that were doing it were of the view that students were going to get higher grades than in GCSE."
Professor Alan Smithers, director of the centre for education and employment research at the University of Buckingham, added that "word has got round that the English IGCSE is easier."
The news comes the day before the GCSE results are published for hundreds of thousands of school children in England, Wales and Northern Ireland.
Last week new figures published by Cambridge International Examinations (CIE) show that the numbers of pupils being entered for its IGCSE in English Language have tripled in the space of a year.
There were 63,000 entries for IGCSE English Language this year, up from 18,000 in 2012.
This year, 61.1% of the students taking IGCSE English Language scored at least a C grade, compared to 83% last year.
The Government announced over two years ago that state schools in England would be able to offer IGCSEs, and that the qualifications would count towards league tables.
The surge in entries follows controversy over the 2012 English GCSE exams.
A row broke out over English grades after last summer's GCSE results were published, with school leaders claiming that tens of thousands of teenagers unfairly received lower-than-expected grades in the subject after grade boundaries were moved between January and June.
Defending the standard of their exams, a spokeswoman for Pearson, which owns the Edexcel exam board, said they "are renowned for being academically rigorous."
"Any candidate who has taken the English Language or English Literature 'Edexcel Certificate' qualification can be assured that this will be recognised as favourably as the GCSE alternative by both HE and employers going forward."
A spokeswoman for AQA added: "In subjects where we have an IGCSE, we ensure we maintain standards with the equivalent GCSE."