From Bulbapedia, the community-driven Pokémon encyclopedia.
The Pokémon Nurse School (Japanese: ラッキー看護学校 Lucky Nursing School) is an anime-exclusive nursing institution intended for Chansey. It was featured in Ignorance is Blissey.
Pokémon Nurse School flyer
When Jessie was young, she wanted to be a nurse. However, she found out that she couldn't get into a regular nursing school, so decided to go to one intended for Chansey. Jessie was competent at nursing, and even showed a Chansey how to properly wrap a bandage. The two quickly became good friends. However, because Jessie was not a Chansey, she fell asleep when her classmates were using Sing to soothe Pokémon, which upset her teacher.
On graduation day, only Jessie didn't receive her nurse hat and egg-shaped pendant, and simply packed her bag and left after watching her friend graduate. As she was leaving, Chansey approached Jessie and offered her her hat, but Jessie refused, so instead she broke the bottom half off of her pendant and gave it to Jessie so they each had something to remember each other by.
Pokémon seen in the Pokémon Nurse School