Abigail Ashford, who is from Bishop's Stortford but attends Chelmsford County High School for Girls, claimed the country's top spot by winning the Junior Girls' Pentathlon, making her Essex School's champion.
The Year 9 student is a member of Chelmsford Athletics Club, with who she trains with three times a week, as well as training twice a week with the afterschool club.
The pentathlon includes hurdles, high jump, long jump, shot putt and 800m.
Another County High School pupil, Year 8 student, Phoebe Smithdale was placed 10th. At 13 years of age this was a highly commendable achievement.
Sarah Bellamy, head of PE at the school, said: "The girls have performed exceptionally well. They have worked extremely hard and we are delighted with their results and well done to them."