0) I think talking about BS/MS/PhD is mostly (95%) the wrong question.
I don't care whether you have a PhD, or no PhD, or two PhDs. I care
whether you know the material and know how to teach.
What courses you've taken is a very poor indicator of what you
know. For example, I have never taken any kind of computer-science
course. I've taught a few, but never taken any.
The same attitude we try to instill in students applies to teachers
as well: Take _personal responsibility_ for knowing the material.
The book, teacher, etc. are there to help you meet the responsibility,
but the responsibility remains yours.
1) I don't think a PhD should be required or expected of high-school
physics teachers. I reckon a PhD is useful, but not overwhelmingly
useful, and it comes at a high price.
I would like to see *some* HS teachers have PhDs, but there's no need
for all of them to. More on this below.
2) This connects to Hugh's excellent rant about appreciating the unity
of the subject. I've seen undergrads who could see the unity ... and
big-shot professors who couldn't. True story: I once was at some sort
of department social event where this Ivy League professor was spouting
"that Ken Wilson, he's so smart, in his lattice gauge theories he sees
the mass gap as being analogous to the cutoff frequency in a waveguide."
Some students behind him were rolling their eyes, saying, "well, duh,
the same equations have the same solutions."
Also: a HS teacher needs breadth, whereas a physics PhD program tends
to be less about breadth than about depth and specialization.
Broad-mindedness is more important than ever, because so much of the best
work is in interdisciplinary fields such as biophysics.
On the other hand, knowledge that is broad but shallow is easily lost.
There are a lot of HS teachers out there who don't know 1/10th of what
was nominally covered when they were in school. See item (0) above.
3) It takes more than a HS education to teach HS physics. That's because
each day there is a decision about how to teach this-or-that topic. One
way will dovetail with more advanced work, and other ways will not, and
you need to know which is which. If you haven't seen the more advanced
topics, you won't know.
Also students pop up with questions beyond the nominal HS curriculum, and
you need to know where to look for answers.
4) There are a lot of schools where a terminal BS or MS gets no respect.
I don't participate in this disrespect, but we need to see it for what
it is.
At some of the big-name schools, they won't even admit you to grad
school if you seek a terminal MS. And yes, they do give out MS degrees
as a booby prize to students who don't pass the admission-to-candidacy
exam.
On the other hand, you should not think that all is lost if you enroll
in such a school and then change your mind. That's because in every
case I've checked, the courses that you would take if you wanted a
decent terminal BS or MS are exactly the same courses you would take
in preparation for PhD work. I've done quite a bit of looking, and I
haven't found anybody who has a curriculum "tailored" to a terminal
BS or MS ... and I don't know what you would change (relative to the
conventional curriculum) in order to "tailor" such a thing.
Of course if you plan on teaching, you can /minor/ in education, but
that doesn't much affect the major course sequence.
I'm not sure you would want to tailor a terminal BS or MS even if you
could. That is because contact with real applications is what keeps
physics honest.
-- People in industry think most academic research is "academic" in the
worst sense of the word, i.e. disconnected from the real world.
-- It is hard to get the professors who do cutting-edge research to heed
the needs of educating undergraduates ...
-- let alone educating high-schoolers.
So in the worst case, HS physics would be fourth on the totem pole, three
jumps removed from cutting-edge real-world applications. Keeping MS-track
courses indistinguishable from PhD-track courses eliminates one of the
possible disconnects.
5) You can promote yourself from fourth place to first place instantly by
getting a summer job in industry. Find a gig where you can apply your
physics skills to real problems.
(To say the same thing the other way, there is something quite perverse
about somebody who learned physics from somebody who learned physics
from somebody who learned physics out of a book.)
Out on the street is where you acquire street cred. This is how you /know/
which parts of the book are true and important, and which parts are hogwash.