More pupils are opting for the "traditional" subjects included in the English Baccalaureate, and the measure is having a major impact on curriculums in schools, figures released by the Department for Education reveal.
The research shows a rise not only among pupils who were in Year 9 when the introduction of the EBac was announced in autumn 2010, but also among those who were in Year 10 - statistical evidence that backs the accusation that schools and parents have persuaded pupils to switch GCSE subjects mid-course.
The English Baccalaureate requires grade C GCSEs in English, maths, a language, history or geography and two sciences. It was introduced by ministers who said they were determined to increase uptake of more "rigorous" and academic subjects.
The measure was used in the 2010 GCSE league tables, which were published in January 2011, revealing that just 22 per cent of pupils took a combination of subjects which could gain an EBac and that 16 per cent achieved the required results. Heads were furious that they were being judged "retrospectively" on a measure that they could have done nothing to prepare for.
The new research, commissioned by the DfE and carried out by the National Centre for Social Research, has assessed the effects of the measure on schools and pupils through a survey of 692 schools. The research, carried out over the summer, found that 33 per cent of Year 10 pupils - those who will sit their GCSEs in 2012 - were taking subjects that could lead to an EBac, while 47 per cent of those taking them a year later will qualify.
It also found that 45 per cent of schools had withdrawn a course or subject or failed to recruit enough students to run it. Those most likely to be withdrawn were BTEC courses, but music, performing arts and textiles were also mentioned, as were some languages.
Around half of schools said the EBac had influenced their curriculum offer and 88 per cent had provided information on the EBac to parents and pupils.
The results will reinforce accusations that the uptake of subjects not included in the EBac, such as RE, music and art, are already suffering.
Rosemary Rivett, executive officer of the National Association of Teachers of RE, said: "It is quite clear that schools are putting pressure on students to shift from RE. Schools are very definitely asking students to change mid-course.
"There are a limited number of lessons in the week. If there are 40 lessons and five go to English, five to maths and five to science, then the space for other subjects, such as RE, music and arts is limited.
"Students who lose out on RE lose out on a subject that explores an area of human life, and human understanding of the world."
The research comes after recent GCSE figures showed that fewer pupils had been entered for GCSEs in geography, history and languages this year compared to 2010. The Government is hoping the EBac will reverse this trend.
Education secretary Michael Gove said: "The numbers studying a proper range of rigorous subjects has been in decline. Now, thanks to our English Bac, that has changed."
A DfE spokesman said: "If since last September schools have increased opportunities for their GCSE students to take EBac subjects - for instance, through making additional courses available - or if they looked again at options with a view to ensuring pupils were given the best opportunity to progress, that can only be a good thing."