Phonics is seldom being used outside primary schools to improve literacy - and older students are falling behind as a result, Ofsted has concluded.
A report by the watchdog also revealed that setting "limited" targets for learners impeded their progress, with white British boys and pupils from poor backgrounds struggling to keep up with their peers.
Despite the success of phonics in helping to "drive up standards in reading and writing" in primaries, the report, Removing Barriers to Literacy, found it was only rarely being used with older age groups.
It said: "Inspectors saw few instances of systematic phonics teaching in the secondary schools, colleges and other providers of adult education and training, despite the fact that for learners without a grasp of the link between sounds and letters, this knowledge is necessary to develop their literacy."
In five of the 22 further education providers visited in the second year of the survey, learners' targets "did not provide suitable challenge".
Effective phonics teaching was found at all of the primaries inspected, with pupils taught "letter-sound correspondences", "how to blend individual sounds together to read words" and "how to break up individual sounds to spell them".
Inspectors observed a "wide variety of effective approaches" using phonics, and there was "no notable difference in attainment" whether schools devised their own programmes or used published schemes.
A national reading test for six-year-olds, due to be piloted in June, has already come under fire from experts, who believe children who cannot read could still perform well.
In the report published today, Ofsted said successful providers understood the "multiple barriers facing children and learners from disadvantaged groups" but found "very few had consistent success in overcoming these barriers for all groups".
In less successful secondary schools, the "limited use of assessment data" for Year 7 pupils led to "insufficiently challenging targets".
"If the targets set for pupils from low-income families are below that of their peers, schools are less likely to succeed in narrowing the attainment gap," the report added.