But it was in her History GCSE where her marks came out top across England and Wales.
Charlie, 16, who has attended the Sleaford school since she was 11, developed her love of the subject when she first started her GCSE course.
She now plans to stay at the High School to study A levels in Biology, German and History and is considering a career in the armed forces.
“I am really, really happy to have done so well but I am surprised. I came out of the exam convinced it hadn’t gone well so to get the highest mark in the country is a shock but a very nice one,” said Charlie, whose sister Lucy also studies at the school.
“A lot of the credit should go to the teachers at the school, though, They were brilliant during the lockdown and were really supportive.
“I’m very much looking forward to carrying on my studies and have already started reading up on the Russian Revolution ready for my A level.”
Mum Amanda and dad Andrew, a teacher himself, said the Billinghay family were very proud of Charlie’s achievement.
“She is always very modest so it comes as no surprise that she thought she hadn’t done that well. We are so proud of her and thankful for the dedication of the staff at the school.”
Head of school Jo Smith said Charlie’s achievement was remarkable and a just reward for such hard work.
“Charlie is a committed, talented and hard working student and truly deserves the recognition,” she said.
“To get the best mark in the whole country with thousands of students sitting the exam is a tremendous achievement and all the staff are very proud of her.
“We are delighted she will be joining the joint sixth form and look forward to seeing her flourish over the next two years.”