Bayley Scales of Infant Development

The Bayley Scales of Infant Development (BSID-II), published by Psychological Corporation, are a set of scales that takes 45 minutes to administer and assess mental, physical, emotional, and social development. Because the scales provide an overall picture of the child’s developmental status, they are often used to evaluate whether children are developing normally or may need further testing to determine if they need intervention or treatment of some kind.

The Mental Scale assesses sensory and perceptual ability, memory, problem solving, learning, and early verbal skills. Sample items include measuring infants’ responses to a bell or to tracking a toy with their eyes. The Motor Scale evaluates physical activities that require the use and of both gross and fine motor skills, including large muscle activities (e.g., sitting and walking) and small muscle activities (e.g., picking up small objects). The developmental level for the status of emotional and social development is assessed through the use of a Behavior Rating Scale (formerly called The Infant Behavior Record or IBR) using a five-point scale. The Behavior Rating Scale assesses variables such as attention and arousal, orientation and engagement, and emotional regulation. The Behavior Rating Scale scores are based on the caregiver’s input as well as the examiner’s judgments. The test is completed by the examiner after the administration of the Mental and Motor Scales and produces a percentile score for comparison to a nonclinical population. Both the Mental and Motor Scales produce a standardized score.

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The test was updated in 1993. Some of the changes include an increase in the age range from 1 month to 42 months, the revision of stimuli, and the addition of almost 50% in new items to reduce racial and gender bias and make the stimuli more attractive to children. New normative data are now available for children with various clinical diagnoses such as Down syndrome and prematurity. The BSID is widely used in research settings, has excellent psychometric characteristics, and has the largest standardization sample of any test.


  1. Black,  (1999).  Essentials  of  Bayley  Scales  of  Infant Development. II. Assessment. New York: Wiley.
  2. Schaefer, E. S., & Bayley, N. (1963). Maternal behavior, child behavior, and their intercorrelations from infancy through adolescence. Monographs of the Society for Research in Child Development, 28(3), 1–127.
  3. Women’s Intellectual Contributions to the Study of Mind and Society. (n.d.). Nancy Bayle Retrieved from