Walkthrough: After Rotom becomes one with your Pokedex, you will be prompted by Kukui to next head to the Trainer School to learn a little bit more about battling and items. Your main objective here is to defeat four trainers found within the school and the schoolyard, as well as the Teacher after doing so.
Wild Pokemon:
initial Pokemon (Levels 5-8): Meowth(50%), Zorua(30%), Magnemite(10%), Grimer(10%)
Level 19 Gastly & Level 19 Drifloon
Trainers:
Youth Athlete Hiromi - Level 7 Bonsly
Youngster Joey - Level 7 Grimer
Preschooler Mia - Level 7 Metapod
Rising Star Joseph - Level 8 Ekans
Teacher Emily (Rowlet Starter) - Level 10 Litten
Teacher Emily (Litten Starter) - Level 10 Popplio
Teach Emily (Popplio Starter) - Level 10 Rowlet
Items:
Exp. Share - Professor Kukui
Potion - Right of Building Entrance
Potion - Left of Building Entrance
Antidote - Left Gated Area
Paralyze Heal - Left Gated Area
Oran Berry - Defeat Preschooler Mia
Quick Claw - Ground Floor Preschooler
TM01 - Defeat Rising Star Joseph
Great Ball - Defeat Teacher Emily
Poke Ball (Hidden) - Near Southeastern Bike Rack
Great Ball (Hidden) - In Middle of Leftmost Battleground
Flame Plate (Hidden) - Near Incinerator
King's Rock (Post Game) - Defeat Principal Asuka
Wise Glasses (Post Game) - From Preschooler (Night) After Solving Mysteries
Post Game
Details: After defeating the Main Storyline, you can return to the Trainer School to battle a number of difficult opponents, including the Principal and Captain Ilima himself.
Trainers:
Youth Athlete Deedra - Level 14 Growlithe
Black Belt Duane - Level 56 Primeape, Level 56 Heracross
Vaporeon User Polly - Level 55 Vaporeon
Principal Asuka - Level 57 Granbull, Level 57 Stoutland, Level 57 Arcanine
Captain Ilima - Level 60 Gumshoos, Level 60 Smeargle, Level 60 Komala