Before revision: The Bayley Scales of Infant and Toddler Development ( Bayley-III is the current version ; version 4 is due to release September 2019) is a standard series of measurements originally developed by psychologist Nancy Bayley used primarily to assess the development of infants and toddlers, ages 1–42 months.
After revision: The Bayley Scales of Infant and Toddler Development ( version 4 was released September 2019) is a standard series of measurements originally developed by psychologist Nancy Bayley used primarily to assess the development of infants and toddlers, ages 1–42 months.