Developmental Stages and Milestones of Child Development Often,
developmental stages are defined by milestones. A milestone is a
sort of marker that tells you where you are while traveling. The
term is drawn from literal stone markers that were used to mark
the passage of each mile on early roads. Today, the term
milestone is used more figuratively, to indicate that a
developmental stage has been achieved. Often, special milestones
mark children's accomplishments, such as walking in infancy and
entering school in early childhood, and these milestones can
help mark children's movement inside and between developmental
stages. Children build new skills and developments on top of old
skills and developments from stage to stage; each stage is
cumulative. A child is able to run bases in a game of baseball
in the middle childhood phase because she was first able to walk
near the end of her infancy stage. Entry and exit from the
various developmental stages tends to occur at particular ages.
Often, a child's stage of