At a given moment, perhaps one-fifth of the students would be doing computer-based lessons and exercises aimed at a deep and durable grasp of core concepts. Let me pause a moment to stress this: one-fifth of the students. This is another way of saying that only one-fifth of the school day, or one to two hours, would be spent on the Khan Academy lessons (or some future version thereof) and any peer tutoring that it might catalyze. Given the greatly increased efficiency of self-paced, mastery-based learning, one or two hours is enough, and this should ease the concerns of any technophobes out
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