On time to learn
And on a lesser-known facet of Benjamin Bloom, who did do other things in the course of a long career.
As Lee Shulman points out, "mastery learning" rose and fell. It had quite a lot going for it, and to a large extent, our Adult Basic Skills programmes in the UK are influenced by it. And Bloom had a serious point, as does Shulman today. And we know that the practicability of responding to their point is limited by timetables and course designs and assessment regimes—and of course funding. But beyond a certain point, how much of the story is about "not enough time"?
Even at the level of basic skills, learning is not simply the incremental acquisition of ever more items of knowledge or skill. At some point it has to involve the capacity to organise and deploy that knowledge and those skills, and that is a different order of learning. As Bateson suggested, and the current thinking about threshold concepts supports, more at the same level will never of itself make the leap.
But we still don't know how reliably to teach this second-order stuff.