The Cheltenham Ladies' College has topped the league for 2012 International Baccalaureate Diploma results.
A 41.0 average point score puts the school into first place, up from second in 2011.
An 18-girl cohort took the assessments and increased the mean result by 1.1 points year-on-year.
The achievement has been recognised with a trophy awarded to the College by the education website www.bestschools.co.uk, which publishes an annual league table.
College IB Coordinator Becky Revell said: "Topping the IB table for 2012 is just reward for all the efforts our girls and teachers have put in over the two year Diploma Programme.
"The College is very proud of everybody involved in the qualification, which educates students across a broad range of subjects."
All the girls who took the exams scored 37 points or more, with 78% achieving more than 40 and one scoring a perfect 45.
College Principal Eve Jardine-Young said: ""We are absolutely delighted to be an IB world school, and are fully committed to the programme as an alternative to A levels in the Sixth form.
"We have had a student achieve full marks in the Baccalaureate in two successive years now, and were proud to have achieved the highest average in the country in the 2012 sittings.
"Reviewing the IB results tables, we are in excellent company with some very strong girls' school representation at the top end.
"Our IB students speak of their learning experiences with genuine passion and enthusiasm, and report that they feel confident about being ready for the demands of university as both independent and reflective learners, used to being challenged and approaching complex situations.
"Now in our fifth year, we are embedding a deep commitment to the values inherent in the programme throughout the school, not least tolerance, intercultural understanding and respect.
"Along with intellectual, physical and emotional balance, these are values which sit harmoniously within the long established ethos of the College."