Ofsted has announced plans to overhaul inspections for more than 1,000 private schools amid concerns that teaching is "seldom inspiring".
Under the changes, made public on Wednesday, inspectors will be looking more closely at a school's leadership and the quality of teaching.
The move will also cut the amount of notice a private school is given of an inspection from two days to half a day.
The overhaul comes following concerns that the quality of teaching in non-association private schools is often simply "competent".
In the 2011/12 academic year, out of 361 independent schools inspected by Ofsted, almost one in four were found to be no better than satisfactory.
Figures from Ofsted's last annual report show that 13% were found to be outstanding, 63% were good, 20% were satisfactory and 3% were inadequate.
Ofsted said that under the new rules, inspectors will make an overall judgment about a school, taking into account pupils' achievement, behaviour and personal development, quality of teaching and the curriculum, pupils' welfare, health and safety and leadership and management.
Ofsted director Susan Gregory said: "The quality of teaching is a key driver of school improvement. One of the main findings from Ofsted inspection last year was that the quality of teaching in non-association independent schools tended to be competent but seldom inspiring.
"It is vital that our inspection is incisive and rigorous, and that judgments are fair, clear and helpful to a school's further development. With this new framework we will focus more sharply on what makes teaching truly effective."
The new inspection rules will come into force next month.
Ofsted is responsible for inspecting around 1,500 fee-paying schools in England that do not belong to an association.
Other private schools are inspected by one of a number of independent inspection bodies.