Mt Pleasant schoolgirl athlete Sarah Carli has produced a sizzling silver medal performance at the 7th IAAF World Youth Championships in Lille, France.Keira High School student Carli, 16, finished second in the girls' 400m hurdles final, in a personal best time of 58.05 seconds.Gold medallist Nnenya Hailey, of the United States, lowered her own World Youth leading performance to win in 57.93.Carli had run 59.67 in her heat, to qualify for the final, which Hailey led from the start.Carli had remained off the radar in the final, running in the outside lane eight, before producing the fastest finishing sprint as she moved from fourth up to silver and record her new PB.Carli's result sees her join Jana Pittman (gold, 1999), Kim Crow (silver, 2001) and Lauren Boden (silver, 2005) among Australian 400m hurdles medallists at these championships."I did not see that coming, especially from the outside lane," Carli said."I'm just so excited, there are so many people that got me here - my coach, my family, this team - and to have a medal is just unbelievable."This was Carli's first time representing Australia.Carli is an Illawarra Academy of Sport scholarship holder."No-one understands how excited I am right now," she told her hurdles coach Mel Logan.Kembla Joggers Club captain Murray Smith praised her performance."Sarah had great success as a middle distance runner a few years ago while still keeping up the sprint hurdles," Smith said of his fellow Kembla Jogger."In the last couple of years she has found that a mixture of her natural speed, and endurance training has directed her towards the 400m hurdles."Sarah always has such a positive vibe about her and I'm sure this tenacious and talented young lady will only keep improving after this confidence boosting performance."