Emmanuel, 14, made his mark despite dominance by Asian countries such as China and Hong Kong. He is the third South African to win a medal at this event.
This is not his first time breaking records, as he has participated in maths competitions since primary school.
Last year, Rassou beat thousands of older teens to place in the top 10 South African Maths Olympiad for Grades 8-9. He went on to become the first South African to win a bronze medal in the primary school individual category at the IMC in India.
Reacting to his son’s achievement, Emmanuel’s father Patrice Rassou beamed with pride, saying he was “extremely proud of his child for holding his own among the world’s best”.
Emmanuel’s determination has not faltered, despite the loss of his mother on Mother’s Day earlier this year, said his father.
Emmanuel combines his gift for numbers with passion and the help of a “great maths teacher”, he said.
In preparation for the event in Bulgaria, he was committed to reading in his own time and getting assistance from his maths teacher. The school has been his main source of support.
Over the past decade, only three medals have been won by South Africans at this event - last year Emmanuel won a bronze for the junior category for primary schools (the first time ever that a South African won a medal in the primary school individual category).
His high school bronze medal this year (even though he is a Grade 8 competing against much older kids) is only the second time a South African managed a medal, with Emmanuel being the only South African with medals for both the primary and secondary school category in succession, said his father.
His son has his sights on winning the final round of the SA Maths Olympiad at the end of this month and other African competitions. He hopes to place higher in international competitions.
Emmanuel arrives in Cape Town on Saturday morning.