Animal Advocacy Careers recently did a literature review of leadership practices. One interesting thing they found was that all leadership styles are basically equivalent – even styles which were specifically constructed to be bad. In particular: “transactional” leadership, which was constructed to contrast with the (presumed better) “transformational” leadership, did not result in significantly different outcomes.
This agrees with my experience: there are certain “obvious” things leaders should do (e.g. establish trust with their reports), and any reasonable leadership style will have some way of accomplishing those things. However, the way in which you accomplish those things varies dramatically between styles. Furthermore, which style is better in any given scenario depends on a bunch of small, idiosyncratic details (and in many cases we can’t even say whether one style is better than another).
This leads me to the following question:
There are leadership practices which we have solid evidence for being robustly good (e.g. “don’t harass employees”). There are also leadership practices which are disputable or nonobvious (e.g. “have a daily standup meeting”). But are there any leadership practices which are both robustly good and disputable?
One reason this matters is that only principles which are both robustly good and disputable seem worth teaching: if a principle is only useful in specific circumstances, it’s hard to generally recommend it to managers-in-training. And if it’s not disputable, then you don’t really need to spend much time teaching it (because it’s “obvious”).
re: Appendix — you might be interested in “The Impact of Consulting Services on Small and Medium Enterprises: Evidence from a Randomized Trial in Mexico”, Bruhn et al 2018. h/t Gwern's August 2020 newsletter.