Bayley Scales of Mental and Motor Development: Foundational infant developmental scale

About the Bayley Scales of Mental and Motor Development

Until the late 1920s, intelligence assessment focused exclusively on school-age children and adults. There was no standardized instrument for assessing infant and toddler cognitive development. Nancy Bayley at the University of California, Berkeley set out to fill this gap as part of the Berkeley Growth Study, one of the first longitudinal studies of cognitive development.

Bayley developed three scales: a Mental Scale measuring early cognitive development (language, problem solving, social-cognitive), a Motor Scale measuring physical milestones (head control, sitting, walking, fine motor control), and an Infant Behavior Record measuring temperament and behavior. The Mental Scale was the most influential and shaped every subsequent infant cognitive assessment.

The Bayley Scales went through major revisions in 1969 (Bayley Scales of Infant Development), 1993 (BSID-II), 2006 (Bayley-III), and 2019 (Bayley-4, current). It is the most-used infant developmental assessment worldwide and is used in clinical practice (developmental disability screening), in research (developmental psychology studies), and in early intervention services. The 1933 original is the historical anchor of this whole tradition.

The 3 subtests

Source

All test materials and historical content on this page are transcribed from:

Bayley, N. (1933). Mental Growth During the First Three Years: A Developmental Study. Berkeley: University of California Press.

Early editions are public domain. Nancy Bayley (1899-1994) was at the Institute of Child Welfare at the University of California, Berkeley. Her work on the Berkeley Growth Study (which tracked the cognitive development of children from infancy to adulthood) was the basis for the Bayley Scales.