A narrow-minded adherence to synthetic phonics as a teaching tool can undermine pupil progress, an Ofsted report has cautioned.
Synthetic phonics is a teaching technique for reading that focuses on the link between letters and sounds.
The report, Reading by Six: how the best schools do it, will be seen as a warning to Conservative ministers, who are committed to the universal use of synthetic phonics to drive up reading results in primary schools.
The Ofsted investigation is not critical of the method as a whole - saying it is key to achieving high standards - but it warns that "some of the tenets" are in danger of introducing an "artificial ceiling" and reducing "the motivation of children who want to explore books".
The Ofsted authors found that the systematic teaching of phonics was key to achieving high reading standards. And after visiting 12 outstanding schools, they also praised schools that had adapted schemes in a "pick-and-mix" approach.
Five schools combined elements from different schemes such as Read Write Inc, Letterland and Jolly Phonics to create their own teaching methods.
The report also points out that monitoring schools' compliance to a single scheme can obscure the fact that the approach may not actually be working.
It found that "some of the tenets of synthetic phonics, such as inflexibly adhering only to decodable books (books which only include certain words) until the child no longer needs formal systematic phonics teaching, could introduce an artificial ceiling and reduce the motivation of children who want to explore books and take on the challenge of reading for themselves".
The findings come just weeks after the Department for Education published advice on the key features of effective phonics programmes. School minister Nick Gibb has been a long-term advocate of synthetic phonics and has called for it to be made compulsory.
But the Ofsted report makes clear the key to success lies in the quality of teaching and leadership.
At Kingsley Primary, Hartlepool, Ofsted described the approach to teaching reading as complex, quirky and effective. Teachers use Letterland, Letters and Sounds, Jolly Phonics and the school's own colour-coded reading scheme.
Head Alison Darby said: "Every time something new comes out, we look at it to see if there are parts which are useful, but we keep the things we know will work. One size does not fit all."
David Reedy, president of the UK Literacy Association, said: "There is a simplistic view of what children need to do. Nobody denies the need for a systematic phonics programme but it is not the be-all and end-all of teaching reading."