Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
The instructor therefore should be as kindly as possible at this stage; remedies, which are harsh by nature, must be applied with a gentle hand: some portions of the work must be praised, others tolerated and others altered: the reason for the alterations should however be given, and in some cases the master will illumine an obscure passage by inserting something of his own.
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.