I think you're trying to say that good researchers will tend to be good teachers. In my experience, there is very little correlation between research output and

I think you're trying to say that good researchers will tend to be good teachers. In my experience, there is very little correlation between research output and undergraduate teaching quality. (My experience being grad school at two different universities.) You are correct that tenure-track professors will not be "slackers". They will, in fact, work themselves silly. But they are primarily evaluated on their research at research universities, not their undergraduate teaching. They tend to put their energies into what they are evaluated on. Also keep in mind that teaching and classroom management is a skill, one which is rarely taught to young professors. I had a stark realization during my second year of grad school, when we were interviewing a faculty candidate coming straight from grad school: he was interviewing for a professor position, and he did not have significantly more teaching experience than I did.