Theoretical Background and Structure of the Bayley Scales of Infant and Toddler Development, Third Edition


Marites Piñon

Document Type

Book Chapter

Publication Date


Originally Published In

Bayley-III Clinical Use and Interpretation: A volume in Practical Resources for the Mental Health Professional

Page Numbers



The Bayley Scales of Infant and Toddler Development, Third Edition is an individually administered instrument that assesses developmental functioning of children between 1 month and 42 months of age. The Bayley-III contains many features that make it a useful assessment tool for clinicians working with infants and toddlers. It complies with the latest federal, state, and professional guidelines for the assessment of children in schools, and covers a broad age range. Few other measures are available for use with children as young as 1 month to 42 months. The Bayley-III is normed on recent census data, and includes a significant number of children from diverse ethnic groups and parent education levels. It includes a number of children with a varied range of clinical conditions, including fetal alcohol exposure and pervasive developmental delay, thus helping guide professionals who work in early intervention. A number of different scores are available to help the examiner understand the child's information-processing capacity and weaknesses. Scaled scores, composite scores, growth scores, percentiles, and age-equivalents can all be derived.