Ability · Gen 7 · 1 Pokémon
Schooling
If user is Wishiwashi, changes to School Form if it has > 1/4 max HP, else Solo Form.
On switch-in, if this Pokemon is a Wishiwashi that is level 20 or above and has more than 1/4 of its maximum HP left, it changes to School Form. If it is in School Form and its HP drops to 1/4 of its maximum HP or less, it changes to Solo Form at the end of the turn. If it is in Solo Form and its HP is greater than 1/4 its maximum HP at the end of the turn, it changes to School Form.
Schooling was introduced in Generation 7. 1 Pokémon and forms can have it.
Pokémon with Schooling
As a regular ability (1)
WishiwashiSchooling FAQ
What does Schooling do?
On switch-in, if this Pokemon is a Wishiwashi that is level 20 or above and has more than 1/4 of its maximum HP left, it changes to School Form. If it is in School Form and its HP drops to 1/4 of its maximum HP or less, it changes to Solo Form at the end of the turn. If it is in Solo Form and its HP is greater than 1/4 its maximum HP at the end of the turn, it changes to School Form.
Which Pokémon have Schooling?
1 Pokémon and forms can have Schooling: Wishiwashi.
Effect text from Pokémon Showdown (MIT); which Pokémon have it from Showdown's Pokédex, cross-checked against PokéAPI. Unofficial fan site.