From 2015 to 2017, I've taken part in the organization of the Tournoi Français des Jeunes Mathématiciennes et Mathématiciens (TFJM²).

In a few words, it is a competition for french high school students that is closely inspired from the world of mathematical research. The students gather in teams of 5-6 people and have some months to think together about 10 problems without known solution. In the 2-3 days of the tournament, the teams present their results to a jury and make (constructive) critics to the solutions proposed by the others.

For more informations, check out the TFJM² webpage as well as ITYM webpage, the page of the international version of the tournament from which the french one is actually inspired.