Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
That, however, is no reason for refraining from the public correction of faults; for we must take the rest of the class into account, who will believe that whatever has not been corrected by the master is right. The two methods should be employed conjointly and in such a way as circumstances may demand.
Beginners must be given a subject
Sometimes they should be left entirely to their own devices, that they may not be spoilt by the bad habit of always relying on another's efforts, and so prove incapable of effort and originality. But as soon as they seem to have acquired a sound conception of what they ought to say, the teacher's work will be near completion: if they still make some mistakes, they must be brought back under his guidance.