This is a paid asset, but now you can download Modern School Gym for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
Modern School Gym v1.0
School Gym modular asset with low polygonal models for building your game.
The package contains:
20 separate fbx models
20 prefabs with colliders
1 demo scene with lightmaps
All objects have two UVs.