Tens of thousands of clever children are being let down by England's state secondary schools, inspectors have warned.
A culture of low expectations in many schools means that bright pupils are not being stretched and are failing to gain top grades at GCSE, according to a new Ofsted report.
Chief inspector Sir Michael Wilshaw said it was "shocking" that, in some cases, school leaders and teachers did not even know who their most able children were.
He called for parents to be sent annual reports giving information on whether their child is achieving as much as they should be, and suggested that pupils should be put into sets for key subjects such as English and maths from age 11.
A Department for Education spokesman said: "Sir Michael is right - secondary schools must ensure all their pupils, including their brightest, fulfil their potential.
"That's why we are introducing a more demanding and rigorous curriculum, toughening up GCSEs and getting universities involved in A-levels."
Last year nearly two-thirds (65%) of pupils at non-selective secondaries, around 65,000 students in total, gained a Level 5 in English and maths in national curriculum tests at the end of primary school, one level above the expected standard, but did not get an A* or A grade in these subjects at GCSE, Ofsted said.
Just over a quarter of these students, around 27,000, did not get a grade B in English and maths at GCSE.
Sir Michael said the figures are "unacceptable in an increasingly competitive world."
He said: "Too many non-selective schools are failing to nurture scholastic excellence. While the best of these schools provide excellent opportunities, many of our most able students receive mediocre provision.
"Put simply, they are not doing well enough because their secondary schools fail to challenge and support them sufficiently from the beginning."
The achievement of the most able pupils in non-selective secondary schools should be an issue of "national concern", Sir Michael said.
"We want our most able children attending these schools to be the leaders of our society, and to be the political, commercial and professional leaders of tomorrow."
His report heaps blame on many schools for having low expectations of what the best students should achieve, and suggests that secondaries are failing to give the same level of attention to these pupils as they do those who struggle in class.
In 40% of the schools visited by inspectors, the brightest students were not making the progress they were capable of, the report said, and in a few, teachers did not know who the most able pupils were.
Sir Michael said: "The brightest and best young people are not routinely achieving the highest grades because their schools fail to challenge and support them properly from the start of their secondary education.
"Shockingly some of the schools we visited had not even identified who their most able pupils were. This is completely unacceptable."
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He added: "Thousands of the brightest children in the state sector are failing to reach their full potential and depressingly, the group of able pupils who are most likely to under achieve are those from poor backgrounds, particularly boys."
Last year, in a fifth of the 1,649 non-selective secondary schools teaching 11 to 18-year-olds not one student gained a minimum of two A grades and a B in at least two subjects preferred by leading Russell Group universities, the report said.
It suggests that clever students become used to performing at a lower level than they are capable of because they are in classes where the work is pitched at middle-ranking students and does not stretch them.
It raises concerns about mixed-ability teaching and suggests that if schools choose to teach in this way then they need to keep a closer check on whether the work was suitable for bright students.
Sir Michael advocated setting children in key subjects from the first year of secondary school.
"I want to give you my own personal view," he said. "Unless you have well-qualified experienced people who know how to deal with mixed ability then it doesn't work.
"If that's not happening it's much better to move to a setting system."
Sir Michael later added that he would "set from the word go", and that this was what he had done as head of Mossbourne Academy in east London, the position he held before becoming chief inspector.
Setting makes sure that "both ends of the ability spectrum get good teaching", he said.
The report calls for parents to be given a report each year setting out whether their child is on track to achieve as much as they should do in national tests and exams.
It adds that schools should ensure that classwork is challenging and demanding throughout the ages of 11 to 14 so that able pupils can make rapid progress.
Sir Peter Lampl, chairman of the Sutton Trust, said: "Today's report confirms that most non-selective state schools are failing to stretch their highly able students. I welcome the stronger focus that Sir Michael Wilshaw is bringing to this issue. But we need to go further.
"Schools must improve their provision, as Ofsted recommends. But the Government should play its part too by providing funding to trial the most effective ways to enable our brightest young people to fulfil their potential.
Enabling able students to fulfil their potential goes right to the heart of social mobility, basic fairness and economic efficiency."