[1] The original scale is generally considered not to satisfy the standards of rigor currently accepted in the field of psychometrics and is no longer used as an evaluative rubric in the clinical context.
The original scale was based on the normative data that was collected from a carefully conducted longitudinal study of early human development.
In 1964 Dr. Francis Ilg and Dr. Louise Bates Ames, the founders of the Gesell Institute, refined, revised, and collected data on children 5–10 years of age and subsequently in 1965, 1972, and 1979.
The GDO-R is a comprehensive multi-dimensional assessment system that assists educators, and other professionals in understanding characteristics of child behavior in relation to typical growth patterns between 2½ and 9 years of age.
The GDO-R uses direct observation to evaluate a child's cognitive, language, motor and social-emotional responses in five strands: Developmental, Letter/Numbers, Language/Comprehension, Visual/Spatial, and Social/Emotional/Adaptive.
Readers of this Technical Report should possess an advanced understanding of appropriate use and application of assessment tools, methods for conducting test development and methodology in statistics and measurement.
The Gesell Developmental Schedule believes that human development unfolds in stages, or in sequences over a given time period.
[1] Some examples are: The Gesell Developmental Schedule was then able to compare the infant or child's rate of development to a norm that was derived from a previous longitudinal study (see history, above).
Accordingly, the scale would purportedly be able to show that infants and young children who demonstrate behaviors or responses more typical of an older chronological age would have higher intelligence.