Putney High School pupiil Katy-Ann McDonald solidified her position at the top of her class, beating her 1,500m personal best by six seconds.
The U15 runner is clear in the record time stakes by 10 seconds after clocking four minutes 27.14 seconds at the British Milers Grand Prix in Watford last weekend.
Having been invited to run and as the youngest competitor, McDonald achieved her PB against fierce competition from girls many years older than herself.
She would finish the race second behind Kingston & Polytechnic's U20 runner Pheobe Law, loosing out on the top spot by 0.55 seconds.
McDonald said: "I tried to hold my lane, even against seniors, but I would have needed another 10m to get on terms with the winner, but I am still thrilled with the result."
Coach Phil Kissi said: "Katy-Ann's school has been incredibly supportive, working to support both her sporting and academic careers in the same way it works with all pupils.
"That supportive environment has helped to create amazing results like last weekend's, and the amazing results that have made the school one of the best in London."