He sees a butterfly and sets off in chase of it.

When he has gone away from the path among the rocks and bushes as far as his mother thinks is safe, she calls him to come back.

In many cases, if the boy does not come at once in obedience to such a call, he would perhaps receive a scolding.

If he does come back at once, nothing is said.

In either case no decided effect would be produced upon him.
But if his mother says, "Johnny, you obeyed me at once when I called you.
It must be hard, when you are after a butterfly and think you have almost caught him, to stop immediately and come back to your mother when she calls you; but you did it," Johnny will be led by this treatment to feel a desire to come back more promptly still the next time.
_A Caution._ Of course there is an endless variety of ways by which you can show your children that you notice and appreciate the efforts they make to do right.
Doubtless there is a danger to be guarded against.