Ofsted school inspections in England are set to be overhauled, the agency's boss Sir Michael Wilshaw announced yesterday.

Around 60 per cent of schools are rated as "good" by the regulator, and Mr Wilshaw said there was "little point" in sending in teams of inspectors every five years just to confirm that status.

Instead he proposed moving to a system where they would be subject to shorter, more frequent assessment, with full inspections reserved for schools which are failing or on the cusp of being rated "outstanding."

He also suggested that all inspectors be employed directly by Ofsted. Some are currently employed through private companies.

The news elicited mixed responses from unions.

Teachers' union NASUWT cautiously hailed proposals to directly employ all inspectors "as a step in the right direction."

But NASUWT general secretary Chris Keates warned: "This announcement fails to address the most serious issues which schools and teachers have with Ofsted - namely the extent to which inspection is driving schools to focus on preparing for Ofsted, rather than on the needs of children and young people.

"The focus on making judgements about a school's effectiveness through a focus on performance data will actually exacerbate the pressures on schools, encouraging even more data churning."

Association of Teachers and Lecturers general secretary Mary Bousted said the union has "repeatedly questioned the quality and inconsistency of Ofsted inspection teams."

She added: "While most schools won't complain to Ofsted as long as the overall judgement reflects their own analysis, many complain to their unions about the process."