WESTCLIFF High School for Girls is ranked second in the country in a table of the highest achieving pupils.
The grammar school was among 81 highest-attaining schools in England at GCSE level.
All the pupils in the schools listed attained the benchmark standard of five A* to C grades in GCSEs or equivalent qualifications, including maths and English GCSEs.
The average number of points scored per pupil was then used to rank the schools.
Westcliff High’s average was 783.7 points and beaten only by Colyton School, in Kent, where the average was 882.5.
The Echo contacted Westcliff High but headteacher Dr Paul Haymen declined to comment.
James Courtenay, Southend councillor responsible for education and learning, said: “It is a wonderful achievement and goes to show how well the school is run. The school is a great asset to the town. I am really pleased with the results of pupils, especially those from Southend.
“The school is not only able to get amazing results like this, it is also helping with other schools across the town to share their expertise.”
Southend High School for Girls was also placed 14th on the list with an average point score per pupil of 660.