Ofsted has refused to “name and shame” 300 schools it has identified as potentially being guilty of off-rolling because of the high numbers of pupils moving between Years 10 and 11.

But the watchdog has said it will identify off-rolling in inspection reports and vowed to crack down on what chief inspector Amanda Spielman described as the “illegal and unethical removal of pupils from school rolls”.

Ofsted’s annual report shows that 19,000 pupils were taken off school rolls between Year 10 and 11 last year, with around half of these not reappearing on the roll of another state-funded school.

Sean Harford, Ofsted’s national director of education, said the inspectorate has a list of 300 schools where there has been unusual levels of pupils leaving between Year 10 and 11.

However, he told Tes that Ofsted would not be publishing it as it does not “name and shame’ schools based on data.

Mr Harford has said that Ofsted will subject these schools to greater scrutiny and that pupil movement will be a factor in deciding when to inspect schools.

He said that Ofsted’s new inspection framework will allow inspectors to better look at the issue of off-rolling.

He said: “On the data and guidance for inspectors that is where we have been slow off the mark here but we are now seeing even within the current framework reports are coming through now where it is clearly identified, as one of the issues which has seen the school be judged as ‘inadequate’.”

The Ofsted annual report says that the 300 schools with high pupil movement could be examples of off-rolling but “might be attributed to ordinary factors such as several family moves.

Stephen Rollett, curriculum and inspections specialist at the Association of School and College Leaders, said: “The vast majority of school leaders deplore off-rolling and will welcome any action to crack down on this unacceptable practice. It is important, however, that data on high levels of pupil movement is used as the starting point to a conversation and that inspectors don’t go into schools with a pre-conceived notion.

“We are reassured by the approach outlined in Ofsted’s annual report but we will need to see how this works in practice.”

Two months ago, Ofsted said that it had raised the issue of off-rolling with Outwood Grange Academies Trust (OGAT). However, OGAT denied any such conversation had taken place.

Ofsted’s annual report, published today, also raises concerns about the lack of school improvement capacity in some parts of the country and said financial incentives are needed to persuade more good schools to become academy sponsors.