I found that I had to teach the nature of science at both the
undergraduate and graduate levels for the honors class and molecular
genetics class that I taught.  Even at the graduate level the
understanding of science cannot be taken for granted.  It turned into
my one lecture speel.  I'd hand out essays by Richard Feynman and Peter
Medewar on the nature of science for the students to read and then we'd
work on a jigsaw puzzle.  I'd use the puzzle as an example of how
science works.  I'd use those cheap 100 piece kid puzzles that you can
buy at WalMart.  I found that the two puzzles that I purchased had an
identical cut out pattern with different pictures.

The first thing that we'd do is turn over the pieces and I'd try and
get the students to think about the problem.  Just looking at the
pieces, can they come to some sort of idea of what the picture was.
Unless you have sometype of super genius that can assemble the pieces
in their mind the students can only come up with vague ideas of what
the picture might be.  We do this in science all the time.  Even the
assumption that it will make a picture that they can make sense of
should be pointed out to them.  Try and get them to think about what
they are doing.  When they start to assemble the puzzle ask them what
they are doing.  None of the students I've had have tried the random
assembly of just putting any two pieces together.  Get them to
understand that they are hypothesis testing by grouping the pieces by
whatever character that they are using (color, pattern, shape).  Ask
them why their hypotheses fail so often.  Get them to understand the
problem that science deals with when you make assumptions based in
incomplete data.  If they were able to take all the characteristics of
each piece and make a perfect analysis they would never be wrong in
their choice of which pieces fit where, but using the mark I eyeball
and only a limited set of characters you often make mistakes.  You have
to expect to be wrong quite often in science.  You have to be able to
test your hypotheses.

A few students always assemble the edge of the puzzle first.  I point
out that this is just what scientist try and do when they create a
framework and build on it.  We usually get the easiest pieces in place
first and the edges are the easiest pieces to fit because they only
have three interacting sides to consider.  Science does what it can and
builds on it.  About this time someone notices that I've taken away the
corner pieces.  When they ask for the corners I ask them how they know
that the puzzle has corners.  It isn't a trick question.  We make
assumptions like this all the time, and it is based on our experience,
but they can also see that some pieces are missing based on their
expected square side and only two interacting edges.  They have an
hypothesis that something is missing and it is based on their
experience and the physical evidence.  I throw out the corners and they
have to scratch their heads because I've given them the corners to
another puzzle, but they still fit and they still complete the outside
of the puzzle.  I tell them that science is full of pieces that don't
quite fit, but that are good enough to help us get a better idea of
what it is that we are working on.

As the puzzle gets completed I make them note how the qualitative as
well as quantitative nature of the hypotheses that they are testing
improves as they acquire more knowledge of what the picture looks like.
 The picture never gets perfect because the corners don't match, but it
is obviously good enough to get a pretty good idea of what the picture
is.

I don't think that I've ever brought up creationism or ID in this
lecture, but if you want to you can just state the fact that ID as a
"concept" has never been able to place a piece in the puzzle of nature.
 They have tested quite a few pieces to see if they fit, but there
isn't a single one left in place at the end of the day.  Essentially,
it is a concept with a 100% failure rate upon testing.  The only pieces
left on the board are the ones that haven't been tested yet.  It has
been found to be worse than just randomly picking any two pieces and
trying them to see if they fit.  If any student doesn't believe this,
just ask them for a single piece that ID has placed in our scientific
knowledge.  You won't find a list of these things at the Discovery
Institute because there are no ID scientific successes.  The farce is
that they have lists of scientists that were or are religious and state
their scientific successes without telling anyone that usually these
guys were responsible for kicking out an ID piece from where it didn't
belong.  These guys are known for their scientific contributions and
not their ID contributions.  This is why many scientists define science
in such a way that ID is excluded from consideration.  It simply has
never worked, and it has been a monumental waste of time.  Definitions
like those that exclude ID get put in place to protect the incompetent
from themselves.  Most rational scientist can figure out for themselves
that they can think about ID, but they can't really expect to use it
for anything.  Not a single success and a 100% failure rate upon
testing is pretty convincing to most scientists.

Ron Okimoto