I chose to use IQ in this post instead of a more vague term like "intelligence," but I could easily have done the opposite. I'm happy to do whichever version is less problematic.

I suggest we change focus from IQ to working memory.

Since working memory is a better predictor of ability than IQ, it is more relevant. A state of less (especially verbal) working memory is more easily modeled. And it makes testable predictions about what kind of presentation of information would work for people with it. Repetition becomes very important, as well as multimodal presentation (i.e. figures and graphs). You need working memory to integrate information, so if you don't have much you're grateful for summaries, not just at the end of a chapter but at the end of every subsection. And without much working memory you get lost in a sea of text more easily, so you want frequent reminders of why you're reading this, where this is going and what exactly you're trying to understand in the specific subsection you're in.