The great question in the management of schools is not how you can take _one_ scholar, and lead him forward most rapidly in a prescribed course, but how you can classify and arrange _numbers_, comprising every possible variety both as to knowledge and capacity, so as to carry them all forward effectually together.
The extent to which a teacher may multiply his power by acting on numbers at a time is very great.

In order to estimate it, we must consider carefully what it is when carried to the greatest extent to which it is capable of being carried under the most favorable circumstances.

Now it is possible for a teacher to speak so as to be easily heard by three hundred persons, and three hundred pupils can be easily so seated as to see his illustrations or diagrams.

Now suppose that three hundred pupils, all ignorant of the method of reducing fractions to a common denominator, and yet all old enough to learn, are collected in one room.

Suppose they are all attentive and desirous of learning, it is very plain that the process may be explained to the whole at once, so that half an hour spent in that exercise would enable a very large proportion of them to understand the subject.