Institutio Oratoria

But if a boy's composition is so careless as not to admit of correction, I have found it useful to give a fresh exposition of the theme and to tell him to write it again, pointing out that he was capable of doing better: for there is nothing like hope for making study a pleasure.

Different ages however demand different methods: the task set and the standard of correction must be proportioned to the pupil's strength. When boys ventured on something that was too daring or exuberant, I used to say to them that I approved of it for the moment, but that the time would come when I should no longer tolerate such a style. The result was that the consciousness of ability filled them with pleasure, without blinding their judgment.