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ensure accuracy. lends itself to the K-4, 5-8, and 9-12 grade-
level clusters used in the other content standards. In this
standard, however, the boundaries of disciplines and grade-level
divisions are not distinct—teachers should develop students'
understandings continuously across grades K-12. Systems and
subsystems, the nature of models, and conservation are
fundamental concepts and processes included in this standard.
Young students tend to interpret phenomena separately rather
than in terms of a system. Force, for example, is perceived as a
property of an object rather than the result of interacting
bodies. Students do not recognize the differences between parts
and whole systems, but view them as similar. Therefore, teachers
of science need to help students recognize the properties of
objects, as emphasized in grade-level co