The Bayley Scales of Infant and Toddler Development (version 4 was released September 2019) is a standard series of measurements used primarily to assess the development of infants and toddlers, ages 1–42 months.

This measure consists of a series of developmental play tasks and takes between 45 – 60 minutes to administer and derives a developmental quotient (DQ). Raw scores of successfully completed items are converted to scale scores and to composite scores. These scores are used to determine the child’s performance compared with norms taken from typically developing children of their age (in months). It has cognitive, language, motor, social-emotional development and adaptive behaviour components.

It has been used in NMD to capture change in young children and infants with SMA and DMD.

A book about BSID is available to purchase on Pearson’s website.