Mencius - Book 4, Part 1, Chapter 18

Kung-sun Ch'âu said, 'Why is it that the superior man does not himself teach his son?'

Mencius replied, 'The circumstances of the case forbid its being done. The teacher must inculcate what is correct. When he inculcates what is correct, and his lessons are not practiced, he follows them up with being angry. When he follows them up with being angry, then, contrary to what should be, he is offended with his son. At the same time, the pupil says, 'My master inculcates on me what is correct, and he himself does not proceed in a correct path." The result of this is, that father and son are offended with each other. When father and son come to be offended with each other, the case is evil.

'The ancients exchanged sons, and one taught the son of another.

'Between father and son, there should be no reproving admonitions to what is good. Such reproofs lead to alienation, and than alienation there is nothing more inauspicious.'
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.