Outstanding schools that are failing their poorest pupils face losing the top ranking, Sir Michael Wilshaw has said, as he warned that an "unseen" group of children were being let down by a mediocre education.
In a new crackdown on under-performance, teams of inspectors will be sent back into schools that are not doing well by disadvantaged youngsters, the Ofsted chief inspector said.
In a major speech, Sir Michael launched a stinging attack on schools in affluent areas of England, particularly in the East and South East where he said poorer pupils faced a culture of low expectations and were left languishing "unseen".
He said it was time to "shine the spotlight on these children and bring them out of the shadows".
"Many children from poor families live in urban areas of social and economic disadvantage and go to schools serving concentrations of such pupils," he said.
"However, many don't live in this kind of place at all. Often they are spread thinly, as an 'invisible minority' across areas that are relatively quite affluent."
The worst place to be a child from a poor family in terms of education was not a major city, but West Berkshire, Sir Michael said.
"Disadvantaged children in this lovely, affluent part of south east England last year had the worst attainment in the whole country at primary school, the second worst at secondary school, and were in one of the bottom three local authorities for qualifications at 19.
"West Berkshire is an example of a much wider problem affecting the relatively prosperous counties of south-east England. On the surface, the overall outcomes for these areas may look good but, for children eligible for free school meals, they hide deep and shocking failure."
Sir Michael said that in future Ofsted would be "tougher with schools which are letting down their poor children", adding: "Schools previously judged outstanding, which are not doing well by their poorest children, will be reinspected."