I believe it is well covered, and indeed all have something to add...
As to my area....I did teach a few classes as a part time instructor in a university program, where any with a general ed degree..(My second was a Bac Mus ed...) would be expected, and should be qualified to teach such as counterpoint, theory, and orchestration...etc..That doesn't mean I am better at it...I just have some experience in working with different students, AND instruments...My masters was also education...(Them that can't..., teach...

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This is the reason I always encourage those that are learning to learn the "basics" ONLY on many instruments ...Then you know such things as range...(To be extreme, for example, you wouldn't want to score the piccolo in the register where you would see the euphonium....) and so on...
It helps to read about, and then go to a source such as a friend, school program, music store, and try to play the instrument...any instrument..buy an old one and try it...then sell it...I never meant to suggest becoming proficient on many instruments...
I think you will find people from back in my time play several instruments poorly, and usually one or two quite well; it was not uncommon, and makes for a better understanding of the orchestra and also band....(I can truly drive you underground with the clarinet, violin and oboe...I play flute however, fairly well...

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This having been said, it is likely any with, again, a general education can learn, and to some degree, teach orchestration...as long as you have GOOD precedents, and many have been mentioned here, starting with Stravinsky....after all, what is teaching?...It is showing and describing something you know, to some level, to someone else...

The real teaching is done by the student...to his or her self.....

John