The inherent difficulty in the experiment of special and appropriate
co-education is the difficulty of adjusting, in the same institution,
the methods of instruction to the physiological needs of each sex; to
the persistent type of one, and the periodical type of the other; to
the demand for a margin in metamorphosis of tissue, beyond what study
causes, for general growth in one sex, and to a larger margin in the
other sex, that shall permit not only general growth, but also the
construction of the reproductive apparatus. This difficulty can only
be removed by patient and intelligent effort. The first step in the
direction of removing it is to see plainly what errors or dangers lie
in the way. These, or some of them, we have endeavored to point out.
"Nothing is so conducive to a right appreciation of the truth as a
right appreciation of the error by which it is surrounded."[32] When
we have acquired a belief of the facts concerning the identical
education, the identical co-education, the appropriate education, and
the appropriate co-education of the sexes, we shall be in a condition
to draw just conclusions from them.

The intimate connection of mind and brain, the correlation of mental
power and cerebral metamorphosis, explains and justifies the
physiologist's demand, that in the education of girls, as well as of
boys, the machinery and methods of instruction shall be carefully
adjusted to their organization. If it were possible, they should be
adjusted to the organization of each individual. None doubt the
importance of age, acquirement, idiosyncrasy, and probable career in
life, as factors in classification. Sex goes deeper than any or all of
these. To neglect this is to neglect the chief factor of the problem.
Rightly interpreted and followed, it will yield the grandest results.
Disregarded, it will balk the best methods of teaching and the genius