Hundreds of secondaries, including many top private schools, have seen their GCSE results plummet to zero following a shake-up of annual league tables.
Under the Government's overhaul, some combinations of English GCSEs and some international GCSEs - often known as IGCSEs - do not count in the rankings.
As a result, many secondaries which took these qualifications have seen their results drop in a key government measure of school performance.
An analysis of the statistics suggests that around 335 schools registered 0% for the proportion of pupils gaining at least five C grades at GCSE including English and maths.
The majority of these are private schools, which tend to favour IGCSEs, including well-known names such as Rugby School and Uppingham School.
Speaking ahead of the publication of the rankings, Richard Harman, chair of the Headmasters' and Headmistresses' Conference (HMC), which represents around 270 leading independent schools, said: "The decision to drop IGCSEs from the league tables over the next two years means those tables have become a nonsense. Several of the UK's most highly performing independent schools and others offering this excellent qualification will now appear to be bottom of the class in the Government's rankings.
"This obviously absurd situation creates further confusion for parents as they cannot compare schools' performance accurately and transparently."
Mr Harman, who is also headmaster of Uppingham School, said: "Many HMC schools will continue to offer the IGCSE as experience tells us it is rigorous and offers a good basis for sixth form study. We know what works for our pupils and will always continue to provide a range of the best and most suitable courses, regardless of the vagaries of political decision making."
The Department for Education said that the reasons schools may report 0% in the key five A*-C measure include:
- Entering students for combinations of English GCSEs such as an English literature course and a combined English course. The DfE argues that students who take English literature separately should also be able to study English language GCSE separately.
- Entering pupils for "unregulated" IGCSEs.
A DfE spokesman said: "We have made important changes to a system that rewarded the wrong outcomes. We have stripped out qualifications that were of little value and are making sure pupils take exams when they are ready, not before.
"The changes may result in some variation across all types of schools, ensuring they are held to account for the right outcomes. We issued guidance to all schools on this."