Here are some subjects I think they would teach at Beacon Academy.
First the confirmed classes:
1. Whatever Glynda's class is. (Combat Sparring?)
2. Grimm Studies
3. History
4. Whatever Peach's class is. (Herbology?)
Then the speculative classes:
5. Weapons (Building Weapons, Maintaining Weapons, etc.)
6. Dust (Probably similar to Chemistry Classes IRL.)
7. Aura and Semblances (This two things would most likely be taught in the same class because semblances are an extension of someone's aura if I remember correctly.)
8. Economics (Not sure if Huntsmen/Huntresses need to necessarily know this, but I think it might be useful to hunters in certain situations.)
9. Fitness/Survival/Gym (This is definitely useful for a Hunter's line of work.)
That's all I can think of at the moment. There are probably more subjects worth teaching to hunters-in-training than what I listed. So feel free to add more classes to this list.