Almost a fifth of A-level entries from private school teenagers achieved the highest grade this year, figures suggest.
Just under half of exams scored at least an A, according to data published by the Independent Schools Council (ISC).
The figures show that, in total, 18.3% of A-level entries from 423 ISC schools were awarded an A* - the very highest grade, compared to 8.3% achieved by all students nationally.
Around 47.9% of A-level entries from teenagers at fee-paying schools scored at least an A grade.
Last year, 17.9% of private school A-level exams were awarded an A*, and around 48.7% achieved an A or A*, although these are not directly comparable with this summer's figures as the data covered a different number of schools.
Information was collected from 452 fee-paying schools in total, covering almost 35,000 students, including those taking other qualifications such as the International Baccalaureate.
Providing the information is voluntary and not all fee-paying schools do so.
National figures for all students in England, Wales and Northern Ireland, published last week, show that 26.3% of A-level entries scored an A* or A this summer, up 0.5 percentage points on 2016.
It is the first time the A*-A pass rate has risen since 2011.
The rise comes amid major changes to the qualifications, with the first grades awarded in 13 subjects that have been reformed, with a move away from coursework and modular exams throughout the course, making them more challenging for students.
ISC chairman Barnaby Lenon said: "Once again, pupils at ISC schools have achieved an impressive set of Year 13 exam results, with the headline A* and A figures remaining particularly strong."