I've written a few times about analogies and metaphors of education. One of the most common these days is "don't reinvent the wheel." This is the sort of advice that sounds wise on first listen, but becomes almost meaningless the more you think about it.
Its meaninglessness is wrapped up in what it implies--that somehow a teacher can import something--the "wheel"--into a class and that doing so will save time and money. This is a key assumption behind the open content movement. But I've wracked my brain, and cannot think of any "wheel" that reduced my time commitment because it was so easily applied to the course.
Instead, in my experience importing something into my teaching means one of two things:
1. I simply shift the time and location of the effort from one place to another. So, for example, when I have incorporated a new textbook into a class, it shifts where I spend my time, moving it earlier in the sequence. Or, I re-allocate resources away from one thing (say, preparing class presentations) to another (becoming familiar with the textbook).
2. I take that thing--a textbook, a pedagogy, some technology, an approach to mentoring--and over the course of the semester my experience with students requires that I re-create the thing itself. I drop chapters that don't work, change topics, spend more time on working with students and less on course content, whatever. By the end of the semester, the "wheel" and the course look substantially different.
Now, I know it is possible to do neither. My dissertation advisor, for example, used the same lecture notes for his intro to US History course in 1995 as he did in 1969. But I expect that most good teachers re-invent the wheel every time they enter the classroom. Perhaps it is because they are guided by another phrase--"you can never step into the same river twice."
Is this a good thing?