This rule is very simple. Use directive style teaching only for content which is reinforced in the productive world in the next seven days.
There are two reasons for this:
First, it keeps a formal curriculum from spiraling out of control into the highly theoretical, legacy, or adult pet projects.
Second, knowledge (and especially "learning to know") decays quickly. So even if you do learn something theoretically interesting, since it is not reinforced, you forget most of it anyway. Teachers often say, "it is frustrating when students come back from vacation because they forget everything." What they mean as a shared complaint is a sweeping and devestating critique of the entire school system.
Now, a great result of this philosophy is that it should not simply impact what is formally learned, but also encourages more activities, be it meaningful work or microcosms. For example, math should be subsequently applied to managing a budget for a project. Working on writing then is reinforced by blogging news articles.