All schools will face no-notice inspections from this autumn, the new Ofsted chief announced today.
Sir Michael Wilshaw said the move was a "logical" progression, adding that it was vital that the public had confidence in inspections.
But school leaders warned they had "real doubts" that the plans would improve inspections, and raised concern that the change had been announced without consulting headteachers.
In an interview with the Press Association, Sir Michael, who took up his post as chief inspector last week, said the introduction of new guidelines for inspections provided a "good opportunity" to cut the notice period given to schools.
"We are introducing no-notice inspections for all schools from this September, not just those that are causing concern," he said.
"There are a number of reasons. First of all it's a logical progression from the situation years ago when there was a year's notice, then it was two weeks, and in 2005 it went to two days.
"That's one reason. The second is we have a new framework, which is really important, that's just come in.
"It provides an opportunity for inspectors to do what's really important - going in and inspecting quality, particularly teaching."
Under the new guidelines, inspectors no longer have to spend time going through documentation before visits, he said.
The launch of Ofsted's new Parent View website means that parents do not have to be sent questionnaires before an inspection as they can give their views year round.
"There's no reason why they can't go in and go straight into the classroom in the first hour of the visit," Sir Michael said.
He acknowledged that it was vital that the public has "absolute confidence in the integrity of inspections".
Last week fresh concerns were raised that some schools were attempting to trick Ofsted by using tactics such as sending weak teachers and unruly pupils home when inspectors were visiting.
"We want to make sure that the public views the process as something that's rigorous and robust and there's no question that schools are not going to follow the rules," Sir Michael said.
The "great majority of schools conduct themselves properly", he said, but added that if there is any sense that a school is not, then Ofsted needs to deal with it.
Sir Michael admitted that some schools may be wary of the change, saying: "In my experience, anything that's new is going to be treated with some nervousness by schools."
Once the process is established he said he believes it will be accepted.
Sir Michael said he wants inspectors to spend "as much time as possible in the classroom".
"I don't want them to spend a huge amount of time looking at documentation, there's too much of that, I want them to go in and observe lessons," he said.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said: "We welcome moves to improve the effectiveness of inspection, but I have real doubts that no-notice inspection will accomplish this.
"An effective inspection system is based on mutual trust and respect, not the premise that schools are trying to 'cheat' and need to be caught out. If it is going to lead to improvement, inspection needs to be done with schools rather than used as a beating stick."
He added: "We welcome Sir Michael's commitment to engage with the profession to improve the effectiveness of Ofsted, but that begs the question why he has announced this significant change before that important consultation with school leaders has taken place."