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I wrote:
Teaching is maybe 10% knowing the subject matter and 90%
motivating the students. They could have gotten the subject
matter from books.
... which was more-or-less OK in context, but won't withstand
detailed scrutiny.
John Clement wrote:
...
Incidentally there have been several studies that showed thatstudents learn
much more when the teacher has better mastery of the subject.So content
mastery is actually a very large factor.
Good point. The percentages I gave are not right in general.
Interestingly, changing the percentages doesn't fix the problem.
The key word here is "factor" (in contrast to "term"). That is,
motivating_the_students (M) and subject_area_knowledge (K) are
!!multiplicative!! not additive. Both are required; neither will
make up for a lack of the other. We have
success ~ M*K
(not M+K) so the idea of percentage is not directly applicable.
================
If we now make the (questionable) assumption that things are
differentiable, we obtain
d(success) ~ M dK + K dM
which is additive, so percentages might apply in particular cases.
I suspect the 90%/10% numbers made sense to me only because of
my narrow experience -- I've taught only in situations where I
was very much in command of the subject, so the "K dM" term was
dominant for me. In contrast, if you made me a major-league
baseball pitching coach, or asked me to teach sculpture, I'm sure
I would get a brutally keen reminder of the importance of knowing
the subject.