Primary school children are being taught nonsense words such as 'voo', 'spron' and 'terg' so that they can't cheat phonics tests.
A report by the Department of Education suggested that 'pseudo words' were employed by large numbers of teachers because they require children to read using phonics - the traditional system that breaks words down into individual sounds - rather than simply memorising lists of established words.
Ministers claim phonics is the best way of teaching children to read.
A new phonics test sat by all six-year-olds in England has also been introduced, requiring pupils to read out a list of 40 words including a number of made-up terms.
Opponents support a mix of techniques to teach reading, including the 'whole word approach' in which children are taught to recognise entire words.
But according to a report, 60 per cent of teachers are now using 'synthetic systematic' phonics, up from 53 per cent last year.
The phonics test had identified more than 400,000 pupils who needed extra help to read.
As part of the study, schools were asked how teachers use phonics in lessons, with the 'introduction of pseudo words' cited as the 'most frequently reported change' in the last year.
But some schools admitted they were only introducing nonsense words to help children pass the test.
Some 90 per cent of teachers said they were 'convinced of the value of systematic synthetic phonics teaching'.
Of those schools that made changes to lessons in the last year, more than half introduced made-up words into the classroom, usually for children aged five.
A Department of Education spokesman said: "In the past, far too many children left primary school unable to read properly and continued to struggle in secondary school and beyond.
"Our phonics check is allowing teachers to identify children struggling at an early age so they can receive the extra help and support they need before it is too late."
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