The school seen at the beginning of A Silent Voice seems to be based on Ōgaki Koubun Elementary School in real life.
Image from PV - 00m32s
There's lots of buildings in front of the school so it's difficult to get good pictures. You can see the similarities here though like the trees and flagpoles in front of the building.
Image from PV - 00m07s
This yellow climbing frame is the same as in the movie, but you can't get a picture from the same angle.
Image from PV - 00m37s
The building behind the climbing frame here matches.
This location was visited on 2016/10/14.
If you decide to visit this place yourself, do remember that it is a school still in use and you should NOT enter it.
School official website
Special thanks to the ones who went here before: