Around a third of GCSE entries from private school pupils were awarded an A* this year, new figures show.
In total, a typical teenager attending a fee-paying school scored the equivalent of two A* grades and seven As in the exams, according to an analysis by the Independent Schools Council (ISC).
ISC Chairman Barnaby Lenon said students achieved a high proportion of top results in "hard" subjects, such as maths, the sciences and languages.
The latest data shows the performance of students at 552 ISC schools, and covers both GCSE and IGCSE exams, with the latter becoming increasingly popular qualifications.
It reveals that 32.7% of all entries received the top A* grade, up slightly from 32% last year, while around 60.6% of entries scored at least an A, up 0.2 percentage points from 2013. This is around three times as many as the national average.
And the vast majority (94.4%) of entries from private school pupils achieved at least a C.
National figures for all students in England, Wales and Northern Ireland, published last week, revealed that j ust over two-thirds (68.8%) of entries scored A*-C, up 0.7 percentage points on last summer.
But the proportion of entries awarded the highest grade fell slightly, with 6.7% gaining an A*, down from 6.8% last year. Around 21.3% of entries gained at least an A grade.
The ISC's analysis of the statistics found that just over three-quarters (77.7%) of pupils at its schools achieved at least five A*-C grades this year, including English, maths, science, and a modern foreign language.
And across all ISC schools, candidates achieved an average total of 481.3 points, which is approximately equivalent to two A* grades and seven As.
Mr Lenon said: "The independent sector is celebrating another set of fantastic GCSE results. In a year when results nationally dipped slightly at the top end, the proportion of our entries awarded grades A* and A has risen.
"ISC schools are pleased to use their independence and freedom to continue to offer both the IGCSE and the GCSE in the best interests of their pupils. It is also notable that ISC pupils achieved a high proportion of the top grades in hard subjects such as maths, separate sciences and languages. Many pupils will continue with these subjects at A-level and then university."
North London Collegiate School, a girls' day school, topped the table this year, with 98.81% of entries from 104 pupils scoring A* and A grades.
Girls' schools dominated the top of the results, with eight girls' schools in the top 10, based on A*-A grades.
Bernice McCabe, headmistress of North London Collegiate School, said: "At NLCS, our students are encouraged to flourish in all areas. We ensure that our girls are stretched academically by offering rigorous qualifications such as the IGCSE, and by teaching beyond the syllabus - to engage students in the subject as an end itself. Our supportive, cohesive environment enables girls to tackle challenges with confidence.
"It is also balance between extra-curricular interests and inspiring teaching which helps girls to success and enjoyment. We offer a wide array of extra-curricular activities which range from mindfulness to horse-riding to computer-coding, and when girls come up with their own ideas for activities or projects, we encourage them to run with them."