We use a theme called St Lucie 7 for our school websites, because it’s very extensible and easy to configure (and has a vast array of configuration options).
This is the same theme that the district website uses, and also the same theme that schools like CAST and FPW use.
A demo site can be installed on your school site to get you started with a look that you want. The demo site options are located at https://the7.io/#!/demos