Khan Academy is a non-profit organisation which aims to provide "free, world-class education for anyone, anywhere", with thousands of YouTube videos covering topics like science, engineering, music, history, economics, computing and more.
KA Lite is a free tool which allows downloading the Khan Academy content you need for offline viewing later.
As well as supporting viewing on the local PC, KA Lite can be run as a local server, which means others on the network can connect to the installation and view the content.
Setup is easier than we expected. The package requires Python and prompts you to enter some account details, but a well-designed installer walks you through the process, explains what you can ignore and what you need to do.
At a minimum, you're then able to select the content and course you need, and batch-download all the necessary videos. (Read the screen carefully-- this might be tens of gigabytes of data.)
If you're aiming to be teaching a group of people, then KA Lite goes much further. You're able to create "facilities" (your schools), add students and coaches, track user progress over time and identify areas where they need help.
It's even possible to sync your data with a cloud-based KA Lite Hub, which enables an administrator to track and manage all their offline installations
KA Lite is an excellent tool for enabling offline learning by groups of students (although it also works just for one). Full setup can take a while, but that's no surprise for something which could effectively track hundreds of students across many remote installations, and you can skip many of the more advanced features if you don't need them.