length of period for practice and an optimum interval, but too many
factors enter in to make any one statement. "The experimental results
justify in a rough way the avoidance of very long practice periods and
of very short intervals. They seem to show, on the other hand, that much
longer practice periods than are customary in the common schools are
probably entirely allowable, and that much shorter intervals are
allowable than those customary between the just learning and successive
'reviews' in schools."[4] This statement leaves the terms very long and
very short to be defined, but at present the experimental results are
too contradictory to permit of anything more specific. However, a few
suggestions do grow from these results. The practice period should be
short in proportion as these factors are present: first, young or
immature minds; second, mechanical mental processes as opposed to
thought material; third, a learner who "warms up" quickly; the presence
of fatigue; a function near its limit. Thus the length of the optimum
period must vary with the age of the learner, the subject matter, the
stage of proficiency in the subject, and the particular learner. The
same facts must be taken into consideration in deciding on the optimum
interval. One fact seems pretty well established in connection with the
interval, and that is that a comparatively short period of practice with
a review after a night's rest counts more than a much longer period
added to the time spent the evening before.

There are certain suggestions which if carried out help the learner in
his memorizing. In the first place, as the number of associates is one
factor determining recall, the fact to be remembered should be presented
in many ways, _i.e.,_ appealing to as many senses as possible. In
carrying this out, it has been the practice of many teachers to require
the material to be remembered to be acted out or written. This is all
right in so far as the muscular reactions required are mechanical and