A school in a tough area which has great teachers and a great curriculum could be rated outstanding from September, even if pupils' results are mediocre, says Ofsted.
But the watchdog denies its proposed new inspection framework for England will mean a dumbing-down of standards.
It says too many schools game the system by "teaching to the test" or "off-rolling" lower ability pupils.
But education unions say the plans do not go far enough.
Ofsted says its new framework aims to rebalance the inspection process to make sure that young people receive the best teaching possible.
It says that instead of taking exam results and test data at face value, inspectors will look at how those results have been achieved, whether they are the result of broad and rich learning - or gaming and cramming.
And this could mean less good news for a school in a leafy suburban area that looks as if it achieves high results "but actually when you look beneath the bonnet they're doing this by a narrowed curriculum" and "some naff qualifications", said Sean Harford, Ofsted's national director for education.
"Then actually they are going to get judged down because they should be doing better," warned Mr Harford.
The inspectorate says its own research suggests that some schools are narrowing their curriculum in order to boost results in key exams.
This can mean:
- at nursery, instead of playing with or reading to children, staff write "endless" reports
- at primary school, instead of reading a wide range of books, children focus on comprehension tests
- at secondary school, pupils drop arts, languages or music, as young as 13, to focus on exam subjects
- at college, students are steered towards "popular" courses to boost numbers but not helped to improve their English and maths
Ofsted says the new framework will include a new "quality of education" judgement which assesses both results and the methods schools use to deliver them.
Additionally, schools currently rated good by Ofsted, which now only have to have a one-day inspection every four years, will face additional scrutiny, with their inspections extended to two days.
Another measure will see inspectors no longer using schools' internal performance data as inspection evidence which should help reduce teacher workload.
There will also be greater focus on pupils' behaviour, with separate judgements for pupils' "personal development" and "behaviour and attitudes".
The aim is to keep a check on "low-level disruption in schools" which is of great concern to parents and "the bane of teachers' lives", says Ofsted.
"Two words sum up my ambition for the framework: substance and integrity," said chief inspector Amanda Spielman.
"The substance that has all children and young people exposed to the best that has been thought and said, achieve highly and set up to succeed.
"And the integrity that makes sure every child and young person is treated as an individual with potential to be unlocked, and staff as experts in their subject or field, not just as data gatherers and process managers."
Education Secretary Damian Hinds said the government backed Ofsted's plan calling it "a hugely positive step forward for all our schools".
But education unions were sceptical - Dr Mary Bousted, joint general secretary of the National Education Union, said the practices Ofsted deplored in the document, the narrowing of the school curriculum and teaching to the test, "have been the results of its own enforcement, through inspection, of a range of narrow measures to judge school quality".
Dr Bousted said until these measures were abolished, schools would continue to be judged on results.
The National Association of Head Teachers said the plan did not do enough to allay teachers' fears that schools in tough areas were treated unfairly in inspections and would not remove the disincentive for teachers and school leaders to work in the most challenging schools. .
"It doesn't appear to be the game-changer we hoped it would be," said NAHT director of policy, James Bowen.
"It appears to us that everything that was in the existing framework is still there and new things have been added as well.
"In a sense, its like a rearrangement of furniture. So there will still be enormous pressure on school leaders and schools under this new framework."