Ofsted’s national director for education has insisted that the inspectorate does not have a preferred length for key stage 3 and will not be automatically marking schools down for shortening it.

However, Sean Harford also warned against schools simply extending GCSE teaching over three years.

He suggested that this approach was the “worst-case scenario” for the schools running a three-year key stage 4 as it meant pupils might not study subjects such as art, music or languages again.

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Ofsted has published a new blog post from Mr Harford responding to concerns over whether the inspectorate has a preferred approach to the length of KS3 in its new curriculum-focused inspections.

The watchdog’s new inspection handbook says inspectors will look at whether a curriculum has been narrowed by a school shortening its KS3.

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Mr Harford said: “First of all, there is no ‘preferred length’ of KS3. It’s for schools to decide their own curriculum and how it is enacted across the school.

“The length of KS3 is certainly not a limiting judgement in our handbook. Schools do not automatically get marked down if their KS3 is less than three academic years long.

“We base our final judgement on whether schools offer pupils an ambitious curriculum across their whole time in secondary education - not on the length of any particular stage.

“We’ll be looking at the curriculum as a whole. Whether it’s rich, ambitious and well-sequenced - rather than when each element is delivered.”

However, his blogpost then adds: “That said - and regardless of the length of KS3 - our handbook is clear that inspectors will look at how the school is making sure that pupils have the opportunity to study a broad range of subjects - at the very least in line with the national curriculum.  We want all pupils to benefit from a good, well-taught curriculum.

“In the worst-case scenario of a three-year KS4, a school will simply pull GCSE teaching forward, stretching a two-year course over three.

“This means that for some pupils, choices made at the end of Year 8 are finite. Some will never get the chance to study a whole range of subjects, typically like art, music or languages, again before they leave school.”

Mr Harford said that schools having a “simplistic discussion” over the length of KS3 were probably having the wrong conversation.

He said instead schools should focus  on “what it is you want pupils to learn, and whether your curriculum is rich, ambitious and well-sequenced”.

The blog said that since September Ofsted had judged some schools under the new inspection framework that have had a two-year KS3 as “good” or better.

He said in these schools no subjects were being squeezed out of the KS3 curriculum and KS4 courses were going deeper into content and being broader than the specifications called for by the exam boards. 

He added: “In the words of Indiana Jones, ‘It’s not the years… it’s the mileage’.  We’re interested in the quality, breadth and ambition of the curriculum across a child’s time at secondary school, through both KS3 and KS4.

“If schools can show that they’ve thought about curriculum carefully - that they’ve built a curriculum with appropriate coverage, content, structure and sequencing, and implemented it effectively - then it’s likely inspectors will judge their curriculum favourably.”

Mr Harford also said that a school’s progress in the English Baccalaureate was a factor for Ofsted understanding a “school’s curricular ambition for its pupils”.

However, he said that inspectors would not make a judgement about the quality of education in any school based solely on this.