Generally, I know the concepts he's working on but I've run into a couple problems. First, they don't use textbooks at his school. It's just poorly made slideshows from the teacher that don't clearly explain any topics. So, to get to parity with his understanding, I'd have to hear the teacher explain it.
Second, his work will generally reference names of laws, theorems, etc. that I'm not familiar with. Usually, I'd search for a document, Khan academy video, or some other YouTube video but this has been time-consuming.
I started asking ChatGPT: "Take on the role of a high school teacher in an advanced physics course. Give me a basic explanation of [insert law name here]. Please provide at least two examples and a reference URL."
This has been incredibly useful.