I used my hack time to sign up to Khan Academy, create my classes and explore the content. I was allowed to import classes from Google Classroom but it said I had 0 students: I believe that the students have to accept my invitation via email. I will need to look into this further.
I explored the content and using the search tool it’s very easy to find what resources are available. Make sure that you choose your subject or year group when creating classes because I think this helps the site to select suitable materials for you. Most resources seem to be either instructional videos or short quizzes. You need to then check the suitability of the resource for your class. It seems that the quizzes produce different questions each time they are started which is a bonus.
Below are some screen shots of a quiz and instructional video: