The watchdog’s new chief inspector Sir Michael Wilshaw argued that "the time is now right" to make all school inspections unannounced.
"Ofsted has been moving towards a position of unannounced school inspection over a period of years," he said. "I believe the time is now right for us to take that final step and make sure that for every school we visit inspectors are seeing schools as they really are in the corridors, classrooms and staff room."
Ofsted already conducts some unannounced school inspections – for example where particular concerns are raised about a school. The watchdog also carries out no-notice inspections of local authority safeguarding services, among others.
"Ofsted already has considerable experience in undertaking unannounced inspections and we know it works," Wilshaw explained. "With this further change, parents and all those interested in what is happening in our schools can have absolute confidence in Ofsted’s findings."
He added that the inspectorate’s new "parent view online questionnaire" would allow inspectors to consider the views of parents during inspections, since parents can now share their opinions of their child’s school at any time.
But Russell Hobby, general secretary of the National Association of Head Teachers, argued that the proposals would reduce schools’ ability to engage with inspections and limit the usefulness of checks.
"It [inspection] is supposed to be a joint process and a dialogue that changes the school's thinking rather than merely criticising it," he said. "And it is this engagement which translates inspection judgments into real improvements. Unless inspection leads to such improvements it is a waste of time."
He added that it is often necessary for school leaders to be out of school during the daytime – attending child protection hearings, for example.
"A well-run school functions normally in their absence but it is not appropriate that leaders should not be present at an event with such vital consequences for the school and their career," he said.
Philip Parkin, general secretary of the union Voice, claimed that no-notice inspections would put an enormous strain on teachers and support staff.
"Ofsted inspections are stressful at the best of times, but it would be intolerable to work under the constant and relentless stress of anticipating an inspection at any moment," he said.
"If that is the way inspections are to go, it shows a distrust of, and disrespect for, the teaching profession and signals that the inspection regime has become too overbearing and needs to be reviewed and restructured to make it much more supportive and advisory."
Nansi Ellis, head of education policy at the Association of Teachers and Lecturers, warned that tinkering with the amount of notice for inspections would not improve education for the vast majority of children and young people.
"We also remain deeply concerned about the use of the online parent view questionnaire," she said. "Any survey that allows people to ‘opt-in’ is likely to attract more critical responses than positive ones, and this one is unlikely to reflect the education most children receive at a school."
The details of Ofsted's plans will form part of a consultation, due to be unveiled in the next few weeks.
