So far based on those in the Characters' tabs. Choir and Dueling is in the lead xD

Quidditch: Bora
Astronomy: Armin, Ophelie, Abel
Charms: Alice, Elise
MCreatures: Abel, Skylar
Potions: Skylar, Mary
Divination: Elise
Choir: Bora, Alice, Elise, Skylar, Mary
Dueling: Aiden, Armin, Ophelie, Abel