Ofsted has decided to keep its "outstanding" grade despite widespread calls for it to be scrapped, chief inspector Amanda Spielman revealed today.

But she also wants a rule change to allow Ofsted to routinely inspect outstanding schools.

Removing the top grade could "send the wrong message about aspiration and excellence in the system", she told an education conference this afternoon.

"I know that there are some who would like Ofsted to abandon grades altogether or to move to a pass/fail model," she said.

"For me, that is a decision which must squarely be decided on the basis of whether the current grading system meets our mission of being a force for improvement.

"We will keep this under regular review. But we’ve concluded, on balance, that it is right to maintain the current grading system in the new framework and that is the basis of the discussion I’m having with ministers now as we engage with them on the new framework as a whole."

Teachers prefer a four-grade system to a "more high stakes" pass/fail model, told the Wellington College Festival of Education.

Many teachers feared a pass/fail system would effectively turn a "requires improvement" grade into a "fail", which "could risk deterring more teachers from working in challenging schools," she said.

Parents have also told Ofsted they want to keep the current system. "They like the clarity of four grades in helping them to make informed choices, and as a marker of how well their child’s school is performing," Ms Spielman said. 

Her comments follow a series of calls from teachers and headteachers to remove the "outstanding" grade on the basis it acts as a distraction for schools, creates recruitment difficulties and penalises schools in deprived areas.

When Ms Spielman was named as the preferred candidate for her role two years ago, she told the House of Commons Education Select Committee that she would consider scrapping the top grade.

But on the weight of the evidence she has seen so far, she is unmoved to do so.

She said today: "When it comes to the 'outstanding' grade in particular, a number of school leaders and others from the sector have persuasively lobbied me, and others, to keep it. Their argument is that by losing outstanding we’d send the wrong message about aspiration and excellence in the system.

"For these reasons, I am not yet convinced of the case for change."

However, she wants to remove the exemption that "outstanding" schools currently have from routine inspections. 

The exemption was brought in in 2011 by the Department for Education to allow inspectors to focus resources on under-performing schools.

But it has seen nearly 300 schools go for 10 years without an inspection, according to a National Audit Office report published last month. The NAO report prompted Ofsted to call for the exemption to be lifted.

Ms Spielman said today that the inspection ban, set out in regulations, had "undermined parental confidence" in the system and "also means our inspectors are getting to see fewer examples of outstanding practice".

"I am pleased to say we are engaging constructively with the Department [for Education] on this issue and hope to say more in the future," she said.

Ms Spielman also used her speech to defend the inspectorate's increased focus on the school curriculum, saying: "For me, a curricular focus moves inspection more towards being a conversation about what actually happens in the day-to-day life of schools.

"As opposed to school leaders feeling that they must justify their actions with endless progress and performance metrics."

Inspecting the curriculum "will help to undo the ‘Pixlification’ of education in recent years," she said, referring to the PiXL (Partners in Excellence) group of schools, which discuss ways to optimise league table performance.

Ofsted's work will not be susceptible to political pressure or educational fads, she said. 

The inspectorate is expanding a pilot in which "inspector reading champions" look specifically at how effectively schools are teaching synthetic phonics.

"This team was born out of concerns that there is a not insignificant group of schools, that are generally doing well, but where there are signs that early reading is not as well embedded as it could be," Ms Spielman said.