Teachers in outstanding schools may be exempted from having their lessons observed by Ofsted under a new inspection system being introduced in September.

But schools rated “satisfactory” will, for the first time, face extra mini-inspections. Mini-inspections will also be reinstated for schools given notice to improve.

The move is intended to tailor inspections to individual schools. It follows a declaration by David Bell when he was chief inspector, that satisfactory was no longer good enough to raise standards.

All schools given a notice to improve, previously known as having “serious weaknesses” or “under-performing”, will face a monitoring visit within six to eight months to check on their progress.

Schools judged satisfactory are currently inspected once every three years but, under the new regime, they will be revisited 12 to 18 months after the original inspection to see how they are tackling weaknesses. Schools with more weaknesses are more likely to receive extra visits.

Initially, one in 20 satisfactory schools will receive a monitoring visit, although these will become more common if they prove successful.

Monitoring visits will continue at schools in special measures but inspectors will be get more freedom to vary their extent and focus depending on the school’s progress.

The new system, announced by Ofsted today, is intended to reduce the burden of inspection on high-flying schools and instead focus on those in need of improvement.

From September, one fifth of outstanding schools will be subject to new ultra-light-touch inspections which will involve just one inspector for a single day. If these prove successful, they will be extended to the top 20 per cent of all schools. These will be identified using previous inspection grades, the judgement of local HMI and performance data, including controversial contextual value-added scores.

An Ofsted spokeswoman said that although it was likely inspectors would visit one or more lessons briefly during ultra-light inspections, they might decide not to observe any lessons. Heads said they strongly opposed greater inspection of satisfactory schools but welcomed efforts to reduce the burden on high performers.

John Dunford, Association of School and College Leaders general secretary, said that there was no need for inspectors to observe lessons.

“It should just be a validation of schools’ self-evaluation,” he said.

Today’s announcement follows an open consultation which drew 689 respondents. Four out of five of these backed the introduction of monitoring visits for schools given a notice to improve, and for satisfactory schools that have pockets of underachievement.

Almost 80 per cent supported a lighter-touch regime for high-achieving schools with more than 70 per cent saying inspections should last no more than a day.

Ofsted’s decision to allow inspectors to dispense with lesson observations during one-day inspections comes despite 69 per cent of respondents judging them to be at least fairly important.

Maurice Smith, chief inspector, said: “Ofsted’s new approach is more proportionate to risk and will represent better value for money by focusing on schools where there is underachievement. It also builds on the success of the shorter, sharper inspections introduced in September 2005.”

* jon.slater@tes.co.uk