Marks for speaking to be scrapped from English GCSEs
Teenagers who have already taken some elements of their English GCSEs will find results from them will not count towards their final grade.
Regulator Ofqual said controlled assessments on "speaking and listening" would be removed from English and English Language GCSEs.
Ofqual said the change, proposed earlier this year, had to be made immediately to "protect standards".
But head teachers' leaders say they are "very disappointed" by the timing.
They said it "flies in the face of reason".
According to Ofqual, the present situation means there is "inconsistency" in how schools set and mark the controlled assessments - in effect course work which is carried out in school, under supervision.
In speaking and listening assessments , students might have to prepare a speech and deliver it to fellow pupils and answer questions from them, having studied famous speeches and various techniques used in public speaking.
Their "performance" is usually recorded and marked by their teachers, with exam boards checking the marks given.
Ofqual believes the setting and marking of the controlled assessments is not consistent between schools.
It says the results of the work already under-taken will be recorded separately in results students receive next summer, alongside the GCSE grade, and that speaking and listening will remain on the curriculum.
Chief regulator Glenys Stacey said: "We know that this will be unpopular with many teachers, and will affect students who have already completed their first year of studies, but we think it right to make these changes and to act as quickly as possible because the current arrangements result in unfairness.
"Exam boards cannot be sure that speaking and listening assessments are being carried out and marked consistently across all schools, and we have evidence that they are not. That creates unfairness, and that is unacceptable."
Russell Hobby, general secretary of the National Association of Head Teachers, said: "We are disappointed that Ofqual has chosen to fly in the face of reason in deciding to implement changes to the structure of GCSE English with immediate effect.
"Thousands of students are more than halfway through their preparation for taking GCSE English in 2014, but now face the disruption of having to sit a different mix of assessment processes.
"Those students going into Year 11 who were assessed for speaking and listening last year will feel cheated, having already prepared for something they felt was going to contribute to their GCSE grades."
Ofqual's changes follow a row and legal battle over the grading of English GCSEs in England last year.
Teachers and schools challenged the grading in the courts, saying thousands of students had been unfairly marked down, but they lost the case to Ofqual which said it had acted fairly, to maintain standards.
There had been claims that over-generous marking of speaking and listening tests by teachers contributed to the problem.
Controlled assessments for speaking and listening had been due to count for 20% of the overall GCSE grade, but now will not count for any.
It is part of a move by Ofqual to shift the balance of marks away from controlled assessment.
Controlled assessments as a whole made up 60% of the marks, (20% speaking and listening and 40 % reading and writing).
Formal written exams made up the remaining 40%.
As a results of the changes confirmed on Thursday, from next summer, formal written exams will count for 60% of the marks and the reading and writing controlled assessments will count for 40%.
Mr Hobby said the head teachers concerns "lie less with the rationale for change than with the unfair timing of its implementation".