Those standing have their work done, and done correctly, and those sitting have some excuse or error to be examined.

A new lesson may now be assigned, and the first portion may be dismissed, which in a well-regulated school will be two thirds of the class.

Their slates may be slightly examined as they pass by the teacher on their way to their seats to see that all is fair; but it will be safe to take it for granted that a result in which a majority agree will be right.

Truth is consistent with itself, but error, in such a case, never is.

This the teacher can at any time show by comparing the answers that are wrong; they will always be found, not only to differ from the correct result, but to contradict each other.
The teacher may now, if he pleases, after the majority of the class have gone, hear the reasons of those who were unprepared, and look for the errors of those whose work was incorrect; but it is better to spend as little time as possible in such a way.