The GCSE pass rate for private school pupils rose this year, bucking the national trend which saw the biggest drop since the qualification was introduced.
Some 94.7% of entrants were awarded grades of at least a C, new figures show - a climb of 0.2 percentage points on 2015.
By contrast the national average fell by 2.1 points to 66.9%.
Over a third (34.5%) of GCSE entries from fee-paying school pupils were awarded the top grade of A*, almost five times higher than the equivalent UK-wide level of 6.5%.
And 61.9% of entrants achieved grades A to A* - over three times the national average.
The figures, compiled by the Independent Schools Council (ISC), are based on data from 552 independent schools across the UK.
They include the international GCSE (IGCSE) qualification as well as the standard GCSE.
Barnarby Lenon, ISC chairman, said: "To see an increase in independent school grades across the board is excellent news and testament to all those working hard in our schools - and of course to the young men and women who sat the exams having built towards them for a number of years.
"Set against a decrease in numbers nationally and in an environment where there are efforts to halt grade inflation, this is particularly impressive."
Julie Robinson, ISC general secretary, said: "Once again, the value of an independent education can be seen through the achievements of the students in our schools.
"GCSEs might not be the most popular of exams - and some commentators have questioned the validity of public examinations at this point in a student's education.
"However, our schools put much emphasis on the core subjects of English, maths, sciences and languages, much-prized by universities and employers, so these exams continue to be a formative stepping stone for our pupils."