You must take:
Pokemon Biology (Elm)
Battling (Sycamore)
TMs and HMs (Oak)

Extra classes
Potions: (Oak)
Evolutionary lines: (Elm)
Pokeballs & Technology: (Juniper)
Berries and Effects: (Rowan)
Wild Pokemon Catching: (Birch)
Training Pokemon: (Rowan)
MEGA EVOLUTION: (Obviously Sycamore)
Gym leader training: (Juniper)