Too many young readers are "lost" to a "legacy of poor phonics teaching", Ofsted has found.
In its annual report, published today, the watchdog said that schools are placing "greater emphasis" on teaching phonics, with the reading method "frequently being taught from the start of Reception".
But phonics programmes are "not being implemented consistently well in all schools", Ofsted found.
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"Where schools use a phonics programme that is not supported by resources, including books and sufficient guidance for staff, this often leads to greater inconsistency and a lack of rigour in the teaching of phonics," the report says.
"These schools also find it more difficult to make sure that books are well matched to pupils' phonics knowledge and that staff gain sufficient expertise in the teaching of phonics.
"Lower-attaining readers are not always receiving the right type or amount of support to help them catch up quickly."
The report adds that there are too many "lost" readers in key stage 2 who are "suffering from a legacy of poor phonics teaching".
"This is particularly noticeable in Years 2, 3 and 4 when struggling readers have often fallen further and further behind their peers," it says.
"These pupils' progress is hindered by limited practice or practice not being related precisely to the gaps in their learning. In turn, this means that not only do they then struggle with reading, but they consequently also have difficulty accessing the full range of curriculum subjects in KS2 and beyond."
Ofsted found that leaders in "outstanding" schools "do not settle for phonics screening check results that are in line with the national average".
In the best-performing schools, teaching is "rigorous" and conducted by specially trained staff, the watchdog said.
"In 'outstanding' schools, leaders instil a sense of urgency in teaching the lowest attaining 20 per cent of pupils to read, at both KS1 and KS2," the report says.
"They do not settle for phonics screening check results that are in line with the national average or explain pupils' poor progress by their background."
It adds: "In 'outstanding' schools, books match sounds. This means that children build confidence and fluency from the very beginning of learning to read. Teachers read books aloud to pupils who cannot yet read them and they do not expect struggling readers to read books that include words they cannot read.
"The teaching of phonics is rigorous and is done by staff who have been trained to use the method well, which ensures that they choose appropriate activities so that pupils get lots of practice and keep up with the expected pace of the programme."