Krishan, who studied at Ryde College in Northwood, north London, was awarded a grade C in a GCSE Information Systems exam. The previous record- holder was Nisha Santhirarajah, aged seven, who also attended the college.
"I like doing the work but I have to concentrate on the difficult bits," said Krishan, who celebrated his success with an ice-cream.
He told GMTV that he would like to be a scientist: "I like science, and also an asteroid is going to hit the earth and I want to stop it."
His mother, Neeta, aged 35, who is a travel agent, said he had done all the work for the course in just five months. "So we weren't expecting him to do quite so well."
Teaching methods at the college are based on accelerated learning techniques that enable pupils to sit exams in a shorter time. Dr Ronald Ryde, the college principal, said: "We are extremely pleased that Krishan has passed the exam at such a young age. Yet again we have proved that age should not be a barrier to academic achievement."
In Brent, north-west London, an eight-year-old gained a C grade in Hinduism. Nitsih Upadhyaya attends a Brent primary school, but studied for the exam at a weekly Hindu Sunday school.
Dilip Lakhani, his teacher, said: "He is over the moon. It is an elaborate subject because you have to give essay-type answers. He has done very well for his age because he has had to write in a philosophical way."
Elsewhere, Matthew Brown, aged 16, from Trinity School, Croydon, south London, was one of this year's highest achievers. Matthew scored 12 A*s, but does not know of his success because he is on an expedition to the Drakensburg Mountains in South Africa.
Barnaby Lennon, head of the school, who has faxed Matthew's results to the expedition's base camp, said: "You don't need to be brilliant to get A* grades but you do have to be very diligent to get 12."
Thomas Coleman, from Wallington County Grammar School in Surrey, also gained 12 A* grades, two of them in short courses worth half a GCSE and another GCSE at A.
Some students secured good grades while battling against disability or illness.
Carly Salter, a blind student from Neath, gained seven GCSEs all at B and C grades. Carly, who attends Cefn Saeson comprehensive in Cimla, Neath, used a Braille typewriter and had the questions involving pictures or diagrams transcribed before the exam.
Richard Fletcher, aged 16, who found out two years ago that he was suffering from Hodgkin's disease, a cancer of the lymph glands, scored 10 A*s and an A grade.
Richard, a pupil at Calday Grange grammar school in the Wirral, has to return to hospital every three months for check-ups but has been given the all-clear.
For some pupils, even 10 A*s was not enough. Tom Burgis, from St Ambrose College in Cheshire, achieved 10 A*s and an A in Latin. He said he would have had an A* in Latin had it not been for the World Cup; the exam and England's game against Tunisia kicked off at the same time.
The Manchester United fan said: "It was difficult enough revising with all the build-up but when we sat down as England's campaign was starting, I got distracted thinking about the score."
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