@lookingforward At Ivies, the classroom performance of their TT professors is the least important part of their tenure portfolio. It is all about number of publications, and dollar amounts of grants. As long as you are not to totally messing up in the classroom, you’re good. Also, most faculty can teach 100, 200, and 300 level courses in wide swaths of their field, so there is rarely a case in which a faculty member cannot teach courses that the university requires. However, TT faculty generally have lighter teaching loads and are rarely required to teach service courses in most Ivies. That is for adjuncts and VAPs.
Tenure denial is, therefore, almost never about classroom performance.
When tenure denial is the norm, however, it no longer is because of the faculty going up for tenure, but because of departmental or college policy. I most recently checked out Yale’s Math department, and only one of their full professors was hired as an assistant professor, every single other was hired after being tenured elsewhere. They also only had one associate professor. They did, however, have a bunch of assistant professors, This is not especially uncommon.
So, in 2010, Harvard’s Faculty of Arts and Sciences announced that it is finally changing this policy, and that it would start actually filling its ranks of tenured professors from within. It has only done this to a limited extent so far, perhaps since it is full of full professors, and will only hire TT faculty as these retire or die. However, the fact that they had to officially change this policy indicates that this was the prevailing policy at Harvard until then. I do not know whether other Ivies have started making these changes. I know that the department of Ecology and Evolutionary Biology at Princeton has been promoting from within for a long time, as Yale’s School of Forestry has as well. But these are still relatively rare, and despite Faculty/College/School level policy changes, it will be a while until this change spreads across all departments, if it ever will.
Thing is, if you want to maintain a mass of faculty with many of achievements, it is always less risky to hire them after they have most of those achievements under their belts. Not only are TT faculty a risk, but TT faculty who are under a lot of pressure to succeed will be risk averse. Why try for something that is big and innovative? It will likely not be funded, since funding agencies are notoriously risk averse, as are journal editors and reviewers, which also makes it difficult to publish truly innovative research. So with innovative research it is almost impossible to procure enough funding and to publish enough to satisfy a tenure committee in an “elite” university. It is usually at least 3 publications a year, and a at least $1,000,000 in grant money to be granted tenure on STEM departments in “top” schools (not Ivies).