Before designing a lesson for the Internet or for the face-to-face
classroom it is vital to have developed objectives. We must know what it is
we want the students to do before we can write a lesson to help them achieve
those objectives.

Consider the following objectives:
Understand the concept of gas pressure.
Know how to solve stoichiometry problems.

What do they really mean?
These are objectives that might be found in a typical introductory chemistry
course.
But what do they really mean? When instructors say that they want students
to understand the concept of gas pressure or know how to solve stoichiometry
problems they know more or less, what is meant by that. How do students know
whether or not they understand the concept of gas pressure? Does that mean
performing pressure unit conversions? Does it mean describing how a barometer
works? Does it mean knowing that the relationship between temperature and pressure
is direct? How do they know when they know how to solve stoichiometry problems?
Does that mean only common problems? Does it mean limiting reactant (a type
of stoichiometry problem) problems? Does it mean problems involving density?

Interpreting student responses to those objectives
If we were to ask a student to explain the concept of gas pressure he/she could
say that "Gas pressure is the force the gas exerts per unit area".
Since this is the definition as worded in a typical textbook we can't really
be sure that a student has a grasp of gas pressure or is only quoting a memorized
definition. Unfortunately we cannot look inside a person's head to determine
whether or not they understand gas pressure.

Behavioral objectives
Instructors need to write objectives that are not vague and that produce observable
action. Behavioral objectives are based on an action by the student that
we can measure. "A behavioral objective indicates what the student should
be able to do or say when he has finished the lesson or, over the long run,
when he as completed his education". This quote is from R. C. Anderson
and G. W. Faust, Educational Psychology - The Science of Instruction and
Learning. 1973. Dodd, Mead and Company, Inc.

Rewording the gas pressure objective
Stating what students need to do to demonstrate by action that they "understand" gas
pressure involves stating many different behaviors. Some of them are given
below. There are many more.

Be able to convert pressure given in either units of atmospheres,
mm Hg, inches Hg, torr, or Pa to any of the other units, to the correct number
of significant figures.
Memorize the number of mm Hg in 1 atmosphere, the number of torr in 1 atmosphere,
the number of inches of Hg in 1 atmosphere, and the number of Pa in 1 atmosphere.
Predict whether gas pressure increases or decreases as temperature increases
or decreases.
Predict whether gas pressure increases or decreases as altitude increases or
decreases.
List the parts of a barometer that measures atmospheric pressure.
All the behavioral objectives in the list above describe observable and measurable
activities.

Does statement of behavioral objectives that are measureable
prevent students from developing higher order thinking capabilities?
Evidence suggests that students who have detailed behavioral objectives learn
more than students in classes that do not. Whether or not having a list of
activities that must be mastered stifles creativity and higher order thinking
has not been proven.

The Concept of Entering Behaviors
Entering behaviors are "skills and knowledge, specifically related to
course objectives, which the student possesses before instruction". This
quote is from R. C. Anderson and G. W. Faust, Educational Psychology - The
Science of Instruction and Learning. 1973. Dodd, Mead and Company, Inc. To
produce behavioral objectives that students can achieve, instructors must accurately
understand the entering behaviors students possess. For example, students will
not be able to convert pressure from one unit to another if they cannot solve
an equation for an unknown variable. An entering behavior is solving algebraic
equations with one unknown variable.

What happens if students don't possess the anticipated entering behavior?
What if they cannot solve algebraic equations, but the instructor designs
lessons assuming that they can? Students will not be able to fulfill some
of the behavioral objectives and the lesson will fail.