TITLE: Is making the math learning process deliberately more challenging an effective teaching strategy?
QUESTION [12 upvotes]: I've often come across a view on teaching/learning math to the effect that
forcing students to struggle rather then "spoon-feeding them" (as they put it) 
makes for much more able students in the long run. a combination of 
"what doesn't kill you..."  and "tough love".
I have friends who have been borderline traumatized by college level
lecturers who subscribed to this view (or were just jaded, heartless butchers) 
and they tend to strongly disagree.
Still, I keep hearing and reading this claim and more often then not
from respected and enviably capable mathematicians past and present.
Here are some examples. The first is by Lebesgue.

When I was a rather disrespectful student at the Ecole Normale we used
  to say that 'If Professor Jordan has four quantities which play exactly the
  same role in an argument he writes them as $u$, $A''$, $\lambda$ and $e_{3}'$ Our criticism
  went a little too far but, nonetheless, we felt clearly how little Professor
  Jordan cared for the commonplace pedagogical precautions which we
  could not do without, spoiled as we were by our secondary schools.
  <...>
  Professor Jordan's only object is to make us understand the facts of
  mathematics and their interrelations. If he can do this by simplifying the
  standard proofs, he does so; <...> But he never goes out of his way to reduce the reader's
  trouble or compensate for the reader's lack of attention.

Another (extreme) example is the approach of R.L moore and the so called "Moore Method" of teaching, still alive and kicking in various degrees
of severity.
Here's an excerpt from P.R. Halmos' autobiography "I want to be a mathematician":

Can the mathematician of today be of any use to the budding mathematician of tomorrow? Yes.
  We can point a student in the right direction, put challenging problems
  before him, and thus make it possible for him to "remember" the 
  solutions. Once the solutions start being produced, we can comment on
  them, we can connect them with others, and we can encourage their
  generalizations. Almost the worst we can do is to give polished lectures
  crammed full of the latest news from fat and expensive scholarly journals
  and books—that is, I am convinced, a waste of time.
  You recognize, I am sure, that I am once more advocating something
  like the Moore method. Challenge is the best teaching tool there is, for
  arithmetic as well as for functional analysis, for high-school algebra as
  well as for graduate-school topology.

Lastly, here's a quote from the preface to Mathematics Made Difficult. Although 
the book is written tongue-in-cheek I believe the following passage
is ultimately uttered in earnest:

there is no doubt that an absolute ignoramus (not a mere qualified ignoramus, like the 
  author) may be become slightly confused on reading this book. Is this bad? On the contrary,
   it is highly desirable. <..misleading redaction...> it is hoped that this book may help to 
  confuse some uninitiated reader and so put him on the road to enlightenment, limping along 
  to mathematical satori. If confusion is the first principle here, beside it and 
  ancillary to it is a second: pain. For too long, educators have followed blindly the 
  pleasure principle. This over-simplified approach is rejected here. Pleasure, we take it, 
  if for the initiated; for the ignoramus, if not precisely pain, then at least a kind of  generalized Schmerz

To put this into the form of a concrete question, what does modern research
say about the effectiveness of this approach, is it justified? Or are mathematicians
testifying to it's benefit perhaps just a manifestation of selection bias? 
Update
As suggested, I've asked the question seperately on cogsci.SE
https://cogsci.stackexchange.com/questions/5921/
Update
Two relevent papers:

Designing Effective Multimedia for Physics Education
 by Derek Muller
(TED talk) (Thanks @nayrb)
Fortune favors the bold by Diemand-Yauman & Oppenheimer

Still hoping to hear of more specific research.
Update
Also asked on the new math educators SE:
https://matheducators.stackexchange.com/questions/875/

REPLY [2 votes]: Learning math is difficult; it takes work. Euclid stated this quite nicely: "There is no royal road to geometry." What should teachers do? Encourage, prod, and guide students into doing that work. Obviously, requiring too much or too little isn't good. Any decent teacher will try to find a good balance. 
Of course, a teacher can pointlessly 'make things difficult.' For example, one of my professors is Chinese, and it sure would make learning math a lot harder for me if he taught in Chinese. The purpose of using words (and symbols) is to convey information. Whatever an instructor does cover should be as clear as possible. But sometimes, it is better not to say everything. For this reason, a 'hint' can be much better than a complete solution.