I’ll throw this into the discussion. This customized level of challenge idea has been around a long time. The sociological implications are far from neutral. See below for a circa 1800 example from Gregor Girard’s school:
(from The Mother Tongue, English translation published 1848)
“Providence does not give to all alike” — call me cynical, but this is where this discussion STILL ends up far too often today.
Hapgood 
Ok, I had to reply to this one. I think it is not the same thing. I need to read more on the different meanings of personalized learning both in theory and in practice. But I do know that the general idea of differentiating according to each person is not necessarily the same thing your quote above refers to. Differentiating according to “level” is one thing, but one can personalize in other ways that are less blatantly socially unjust, and are actually more empathetic to student needs and helps them achieve their goals. So to me, the term personalization is the opposite of universalism, and that means things like doing culturally relevant pedagogy and allowing students different pathways to the same goal or sometimes different goals, even. In the abstract. In another post you talked about how unproductive it would be to have a book club with people on different chapters of the same book. Personalization to me means something else: give students choice of which books to read about a particular theme, then meet and talk about the theme, not the book. They’ll all have been introduced to the theme, and small groups working on the same book could have had discussions (structured or not; unstructured discussions have value, too, as people get older; structured discussion can have power issues; debate being one of the best examples of a dialogue with illusions of fairness).
But i need to read more to make sure i am talking about the same thing you’re talking about 🙂
As Michael Feldstein points out, the term personalized learning is so mushy as to be useless, so maybe I should be more specific.
In general, however, in the U.S. when personalized learning is mentioned in the context of tech it almost always is either in the defense of:
1) instructing students at their “own pace”
2) using “learning styles” to teach
3) addressing what are believed to be a wide range of underlying conceptual issues via computer-based diagnosis and remediation.
The other personalization I agree with you — absolutely (although there is still a balancing act between individual and group dynamics). But we’ve been doing that for ages — student presentations on chapters or topics, research seminars, individual projects etc. It absolutely works, and if that’s what Silicon Valley meant by personalization then I’d say Huzzah (or some 21st century expression). They just don’t mean that.
But perhaps these posts are a bit U.S. centric.
Interesting Read