[SamBam]

Your anecdote, especially with it's reference to lectures, makes it sound like you're talking more about higher education. The author is clearly talking about K-12, and mostly pre-high school.

As an educational researcher, I think the author's conclusions are quite likely. A sixth grader isn't going back over their lecture notes and gaining more understanding.

[albert_e]

Watching a Khan Academy video a second time ... is unlikely to help understanding a concept better?

> Still others believe—incorrectly—that more time spent on a task produces better results

Even more foundational skills like reading, writing, speaking, and school math (addition, division, algebra) are unlikely to get better with practice?