Forgetting curve means it's better to learn about independent topics (in lets say philosophy) A B C in the order ABCABCABC, but almost in every school it would be AAABBBCCC.
In a bit more detail, the basic idea is that forgetting is a regular, valuable occurance to have better access to the useful information and the way that useful information is determined is use over time. If you use particular information intensely over a short period of time then stop using it at all, that is a signal that you are done with that information and it will be forgotten fairly quickly. But if you use it again after a while then that is a signal that it might be useful even further into the future. Spaced repetition is another application of this idea.
I've always liked B.F. Skinner's ideas about learning, where the forgetting curve is paired with the idea that making mistakes is quite harmful since then we also have the memory of the incorrect answer (that will decay more slowly than random information due to being close to the thing we want to actually use). So it is better to refer to the correct answer until you can recall it correctly, which happens automatically as a standard brain optimization when we do something repeatedly.
I don't really know anything about direct instruction, but it sounds like a core idea is heavily scripted teacher student interaction, which sounds even more dystopian to me than the current system (like being raised by an automated call center in human form). But IMO a bit further in that direction would be great. Remove teachers from the normal learning loop and provide a variety of learning materals (books, video, audio). Teachers can then assist students individually and spend more time being social workers or whatever else is needed so that kids are in a place to be able to learn. Currently the whole school experience tends towards performance art by teachers where the presence or absence of students is a secondary concern. If learning was the important part then the experience would be centered around learning with the presence or absence of teachers a secondary concern.
