Diagnosable mental defects aside, I refuse to believe that there exist students who genuinely want to learn Java with a private tutor who understands the student's mental model of the world.
Students range from couldn't-care-less to passionate, not from stupid to smart.
I suspect students could be plotted on both axes, and probably several others (amount of background knowledge, for example) as well.
It seems clear that smart/passionate will generally do well and stupid/CCL will generally fail, but that leaves smart/couldn't-care-less (know-it-alls who won't listen to anything in class) and stupid/passionate (who will probably need to put in extra time, but have a good chance).
Everyone will fall somewhere in between, of course - those are just quadrants.
stupid/passionate (who will probably need to put in extra time)
I think this view ignored the correlation between "put in lots of time" and "smart". All of the smart people I know have usually put in an extraordinary amount of time studying whatever they are good at.
Students range from couldn't-care-less to passionate, not from stupid to smart.