hat is too difficult discourages effort, and is, therefore, equally
uninteresting. It should be sufficiently easy for every pupil to master,
and sufficiently difficult to require real effort.

2. The amount of matter included should be carefully adjusted to the
length of time taken for the lesson and to the attainments of the class.
If too much is attempted, there will be insufficient time for adequate
drill and review, and hence there will be lack of thoroughness. If too
little is attempted, time will be wasted in needless repetition.

3. Each unit of instruction in any subject should, in general, grow out
of the preceding unit taken in that subject, and be closely connected
with it. It is in this way that a pupil's interest is aroused for the
new problem and his knowledge becomes organized. Neglect in this regard
results in the possession of disconnected and unsystematized facts.

Each lesson should contain one or more central facts around which the
other facts are grouped. This permits easy organization of the material
of the lesson, and ensures its retention by the pupils. Further, the
pupils are by this means trained to discriminate between the essential
and the non-essential.

CHAPTER XVII

LESSON TYPES

=The Developing Lesson.=--In the various lesson plans already
considered, the aim has always appeared as an attempt to direct the
learning process so that the pupil may both build up a new experience
and also gain such control over it as will enable him to turn it to
practical use. Because in all such lessons the teacher is supposed to
direct the pupils through the four steps of the learning process in such
a way that they discover for themselves some important new experience,
or develop it out of their own present knowledge, the lessons are spoken
of as developing lessons. Moreover, the two parts of the lesson in which
the new experience is especially gained by the pupils, namely the
selecting and relating processes, are often spoken of as a single step
and called the step of _development,_ the lesson then being treated
under four heads: Problem, preparation, development, and application.

=Auxiliary Lessons.=--It is evident, however, that there may be lessons
in which this direct attempt to have the pupils build up some wholly new
experience through a regularly controlled learning process, will not
appear as the chief purpose of the lesson. In the previous consideration
of the deductive lesson, it