History, theories, methods and findings are characteristic
of all disciplines. Also characteristic is the tendency to keep
within a discipline much of what is known from discovery by
scholars in other fields. While unintentional for the most part,
the scant knowledge sharing across disciplines arises from deficits
or uncertainties in understanding the definitions of terms,
references to key constructs and features, variations in
methodologies, and in interpretations of findings. Yet, as the
chapters of this book reveal, much is known across several
disciplines that converge on many of the same developmental
disorders that are (and have been for decades) the focus of
considerable research activity. The extensive interest in the
study of developmental disorders exists both to understand their
natures and causes as well as to reveal differences and
similarities in development across normal and abnormal populations.