and capacity; lacking
this stimulus and guidance, the powers are left crippled and incomplete.

On the other hand is the subject-matter of education, the heritage of
culture which has been accumulating through the ages. In the slow
process of human experience, running through countless generations, men
have made their discoveries in the fields of mathematics and science;
they have lived great events and achievements which have become history;
they have developed the social institutions which we call the State, the
church, the home, and the school; they have organized great industries
and carried on complex vocations; they have crystallized their ideals,
their hopes, and their aspirations in literature; and have with brush
and chisel expressed in art their concepts of truth and beauty. The best
of all this human experience we have collected in what we call a
curriculum, and placed it before the child for him to master, as the
generations before him have mastered it in their common lives. For only
in this way can the child come into full possession of his powers, and
set them at work in a fruitful way in accomplishing his own
life-purpose.

It is the function of the teacher, therefore, to stand as an
intermediary, as an interpreter, between the child and this great mass
of subject-matter that lies ready for him to learn. The race has lived
its thousands or millions of years; the individual lives but a few
score. What former generations took centuries to work out the child can
spend only a few months or a few years upon. Hence he must waste no time
and opportunity; he must make no false step in his learning, for he
cannot in his short life retrieve his mistakes. It is the work of the
teacher, through instruction and guidance, that is, through teaching, to
save the child time in his learning and development, and to make sure
that he does not lose his opportunity. And this is a great
responsibility.

Thus the teacher confronts a problem that has two great factors, the
_child_ and the _subject-matter_. He must have a knowledge of both these
factors if his work is to be effective; for he cannot teach matter that
he does not know, and neither can he teach a person whose nature he does
not understand. But in addition to a knowledge of these factors, the
teacher must also master a technique of instruction, he must train
himself in the art of teaching.

_The teacher must know the child._ It has been a rather common
impression