I appreciate Jules' wonderful quote from Newman (below) on the education of adolescents! It is of prudential importance for universities and their student life policies, of course, but also for all parents, most of whom have a natural tendency toward overprotectiveness. But it is especially relevant--I would think--for homeschoolers.
Perhaps in the modern day, however, it is important to clarify what Newman is talking about when he refers to Aristotle's comments on the "Lesbian Canon" from Nicomachean Ethics, 5, 14. Thus I append the explanation below with a line from the text and the accompanying footnote by Francis Lieber:
chapter xxix.: advantages of institutional government, farther considered. - Francis Lieber, On Civil Liberty and Self-Government 
On Civil Liberty and Self-Government, 3rd revised edition, ed. Theodore D. Woolsey (Philadelphia: J.B. Lippincott & Co., 1883).
Author: Francis Lieber
Editor: Theodore D. Woolsey
It would seem, also, that by a system of institutional self-government alone the advantage can be obtained of which Aristotle speaks, when he says that the psephisma (the particular and detailed law) ought to be made so as to suit the given cases by the Lesbian canon,1 and ought to be applied so as to fit the exact demands.
1 The cyclopean walls in Greece and Italy, built before the memory even of the ancients, and many of which still stand as firm as if raised in recent times, have their strength in the irregularity of the component stones, and the close fitting of one to the other, so that no interstices are left even for a blade of grass to grow. An irregular polygonal stone was placed first; sheets of lead were then closely fitted to the upper and lateral surfaces. When taken off, they served as the patterns according to which the stones to be placed next were hewn. It was this sheet and this mode of proceeding which was called the Lesbian canon or rule, while the canon or rule which the architect laid down alike for all stones of an intended wall was called a general canon. See On the Cyclopean Walls, by Forchhammer, Kiel, 1847. Now, Aristotle compares the general law, the nomos, to the general canon, but the particular law, the psephisma, ought, as he says, to be made by the Lesbian canon. Ethica ad Nicomachum, 5, 14. It is inelegant, I readily confess, to use a figure which it is necessary to explain, but I am not acquainted with any process in modern arts similar to the one used as an illustration by the great philosopher, except the forming of the dentist's gold plate according to a mould taken from nature itself. I naturally preferred the simile of the philosopher, even with an explanatory note, to the unbidden associations which the other simile carries along with it. Nor would I withhold from my reader the pleasure we enjoy when a figure or simile is presented to us so closely fitting the thought, like the Lesbian canon, and so exact that itself amounts to the enunciation of an important truth, well formulated. This is the case with Aristotle's figure.