....well, clearly, all would be much better but I have a specific recommendation to address in this post.
I haven't shared this with many folks, but during my sabbatical I've been taking guitar lessons — I've always wanted to play the guitar and have found a most amazing teacher and am making, I think, some fairly decent progress.
In addition, about 10 years ago, I started taking martial arts classes and progressed far enough to get my red belt (that's one before black in the school I was in). I learned various styles of external martial arts (northern & southern kung fu) and then a variety of internal arts (tai chi, bagua, Hsing I & liuhebafa) — I stopped training about 5 years ago when other things started taking priority in my life.
The point here is that these are two things I started and was, in both cases, an absolute rank amateur (I was studiously not athletic as a child and no one I know would ever call me musical - my mother has told me that I couldn't "carry a tune in a tin bucket" - yes, more fodder for therapy). And in both situations have struggled do learn things that haven't come easily. I think that doing this has made me a significantly better teacher because I've had to work really hard to learn things and have been completely at the mercy of my teacher.
So, here's my recommendation: all teachers should be required to take classes in something completely outside of their comfort zone so they can experience what our students experience.
I think there's also something really important to learn not only in experiencing 'studenthood' but also in watching teachers whose livelihood depends upon students choosing to return. Teachers who work in schools have the luxury of having students who have to show up. Rarely does our paycheck depend upon students willingly showing up. Both my martial arts instructor and my guitar instructor depend upon students who want to come back (and, I presume, on students recommending them as teachers to other potential students). As a result they have to teach in a way that makes the student not hate instruction but that also successfully instructs.
I read loads and loads about teaching theory, educational psychology, developmental psychology, philosophy of education and these two teachers (particularly my guitar teacher) have happened upon the very principles that research has developed.
So, I think all teachers can learn a huge amount not only be being students but by experiencing being taught experiencing teaching from people whose livelihood depends on success.
There you go. That's what I'd do if I were in charge, require all teachers to take classes outside of the comfort zone. We make students do it and we should never do to others what we are unwilling to do ourselves and everyone would really benefit from it.