One of the big three classroom unions has called for a radical reform of the Ofsted inspection system, which would include the abolition of overall grades for schools.

The ATL says it wants a “significant change in culture” that would see inspection teams having a supportive “continual relationship” with schools that only occasionally led to full inspections.

When inspections were conducted, there would be no overall judgement. Instead, a short summary document would be published alongside the full report setting out strengths, areas for improvement and agreed steps to tackle them.

Mary Bousted, ATL general secretary, said: “We propose an inspection system that is tailored to school improvement, proportionate in its impact and works with, not against, the teaching profession.”

The union’s report, A new vision for inspection in education, published today, is only the latest high-profile criticism to hit the embattled inspectorate.

The ATL calls for inspection that is “supportive not adversarial; advisory not dictatorial; empowering not punitive”.

“Self-assessment and professional dialogue would be central,” the document adds. “Data would be used to guide, not decide.”

Last week, Labour leader Ed Miliband said he would take teachers’ concerns about the variable quality of inspections to Ofsted. Meanwhile, the Conservatives, it has been reported, are considering a radical reform of the watchdog if they form the next government.

In April Dr Bousted said Ofsted had become a “laughing stock” among teachers. It was unfit to reform itself but was “so damaged, so tarnished that it has to be radically and completely transformed”, she told her members.

Today’s ATL report calls on inspection teams to be selected to ensure they have expertise in issues likely to be of particular interest at the school they visit. These issues would be identified through pre-inspection evaluations of schools.

Sean Harford, Ofsted’s national director for schools, has responded to some of the union’s criticisms in a blog in which he says that bringing all school inspectors in-house will mean “more opportunity to improve quality through training and quality assurance”.

He also says he that more than half of inspection teams include a serving teacher and that he wants this proportion to increase.

An Ofsted spokesperson said: “Once we have inspected a school we provide an overall grade based on the behaviour and safety of pupils, the quality of teaching and the achievement of pupils, among other criteria.

“We believe this gives an accurate reflection of the school’s standards, and provides clarity for parents, pupils and the school itself. Inspection reports set out the rationale for overall judgements.”

Related stories:

Miliband tells TES: ‘We are offering a new beginning for teachers’ February 19 2015

Ofsted is ‘riddled with problems’ and a ‘laughing stock’ among teachers, says union leader April 16 2014

Ofsted has ‘lost credibility’ with teachers and must improve quality of inspections, union claims April 14 2014