he should go and actually manage elsewhere.
This certainly seems to be the popular view, i.e. that he needs to 'learn his trade' elsewhere.needs to go out into the wild and find a managers job of his own to test himself
In many industries however, apprenticeship is a tried and tested formula.
In principle I see nothing wrong with him learning his trade under a succession of managers here at Everton.
Whether it will work out or not remains to be seen.
I can't recall many reds saying that Paisley or Fagan needed to 'prove' themselves elsewhere prior to their appointments. Neither of them did a bad job from what I remember.