Ofsted warns schools against prioritising exam results over a proper education.
Disadvantaged children are not helped by turning a "blind-eye" to schools that get good exam results but are narrowing education, according to the Ofsted chief inspector.
Amanda Spielman is expected to say on Tuesday that grades are "hollow" if pupils have not received a well-rounded schooling.
Ofsted introduced a new inspection regime last September, which focuses more on the quality of the curriculum and education on offer, rather than exam results.
The inspectorate's annual report, published on Tuesday, is expected to say that while it is early days for the new system, they are seeing schools that give all pupils a broad education.
But there is also a small minority who bend the curriculum to boost their exam results and position in league tables.
Ms Spielman is expected to say: "We must not succumb to the seductive but wrong-headed logic that we are helping disadvantaged children by turning a blind eye to schools that are narrowing education, if they deliver acceptable grades at the end.
"Grades are hollow if they don't reflect a proper education underneath."
Her comments come following criticism last week of Ofsted's new inspection regime by two leading academy bosses.
The chief executives of the Harris Federation and Outwood Grange - which collectively educate tens of thousands of pupils - told the Times they were concerned that inspectors are putting a broad curriculum over properly preparing students for their GCSEs.
They raised particular concerns about the effect on children from disadvantaged backgrounds.
Ofsted's annual report is also expected to raise concerns about science in primary schools.
The subject was removed from national curriculum tests taken at the end of primary school a decade ago.
This move may account for a slight fall in England's science results in international Pisa tests, which are taken by 15-year-olds around the world, the report will suggest.
The inspectorate is expected to say that it understands why science has fallen down the priority list in many primaries, but that some schools are showing there is space in the curriculum to give children a good grounding in maths and English, while building knowledge in other areas.
Published: by Radio NewsHub