lessly remarked by those who are supposed to be wise in educational
matters that it makes no difference how much we forget if we only have
proper drill and training to study. That is, how we study is more
important than what we learn. But viewed in the light of apperception,
acquired knowledge should be retained and used, for it unlocks the door
to more knowledge. _Thorough mastery and retention_ of the elements of
knowledge in the different branches is the only solid road to progress.
In this connection we can see the importance of learning only what is
_worth remembering_, what will prove a valuable treasure in future
study. In the selection of material for school studies, therefore, we
must keep in mind knowledge which, as Comenius says, is of _solid
utility_. Having once selected and acquired such materials, we are
next impelled to make _constant use_ of them. If the acquisition of
new information depends so much upon the right use of previous
knowledge, we are called upon to build constantly upon this foundation.
This is true whether the child's knowledge has been acquired at school
or at home. In order to make things clear and interesting to boys and
girls we must refer every day to what they have before learned in
school and out of school.

Again, if we accept the doctrine that old ideas are the materials out
of which we constantly build _bridges_ across into new fields of
knowledge, we must _know the children_ better and what store of
knowledge they have already acquired. Just as an army marching into a
new country must know well the country through which it has passed and
must keep open the line of communication and the base of supplies, so
the student must always have a safe retreat into his past, and a base
of supplies to sustain him in his onward movements. The tendency is
very strong for a grade teacher to think that she needs to know nothing
except the facts to be acquired in her own grade. But she should
remember that her grade is only a station on the highway to learning
and life. In teaching we cannot by any shift dispense with the ideas
children have gained at home, at play, in the school and outside of it.
This, in connection with what the child has learned in the previous
grades, constitutes a stock of ideas, a capital, upon which the teacher
should freely draw in illustrating daily lessons.

2. The use of our acquired stock of ideas involves a constant _working
over_ of old ideas, and th