The Bayley Child Development Scales were developed by Nancy Bayley et al. In 1933 and revised in 1969. It is a comprehensive means of assessing the development of a child in a particular state following more than 40 years of research and clinical practice with small children. The test was standardized on a sample of 1,262 American children aged two to 30 months divided into 14 groups in the year 1960 and has three versions: BSID I published in 1969; BSID II published in 1983 and the most updated BSID III published in 2006. The BSID II scales are recognized among the best scales in the area of ​​child development assessment, providing reliable, valid and accurate results of the child's state of development. Its use as a research tool has received great support from the scientific community, but its high cost and training required for proper administration explain why its use is almost always exclusive to specialists working with young children.

The Bayley Scale - III is an update of the BSID-II normative data with a contemporary and representative sample, indicated to evaluate children from 1 to 42 months of age, presenting improved test content, improved psychometric quality and, consequently, higher clinical utility. The current version of the Bayley Scale is subdivided into five domains: Cognition, Language (expressive and receptive communication), Motor (thick and thin), Social-emotional, and Adaptive Component. The first three domains are observed with the test child and the last two are observed through questionnaires completed by parents or caregivers. The scales are considered complementary, each having its importance in the evaluation of the child. Thus, the Cognitive Scale determines how the child thinks, reacts and learns about the world around him and is composed of 91 items; the Language Scale is subdivided into two subtypes: Receptive Communication - part that determines how the child rearranges sounds and how the child understands, speaks and directs words, consisting of 49 items - and Expressive Communication - part that determines how the child communicates using sounds, gestures and words, composed of 48 items.

The Motor Scale is subdivided into Thick and Fine Motor Scale. The Thick Motor Scale determines how the child moves his body in relation to gravity, made up of 72 items, and the Fine Motor Scale determines how the child uses his hands and fingers to do something, made up of 66 items. The scale also allows a qualitative assessment of the child's behavior, ie, their attention, understanding of the orientations, task performance and emotional regulation. However, the scale can only be applied by specialized and trained professionals. It is a playful, flexible instrument with an excellent standard of validity and reliability, which allows the early identification of problems or developmental delays and signals the need for further evaluation in a specific area. The Bayley Child Development Scale (Bayley III) indicates the strengths, weaknesses, and competencies of the infant or child for proper planning of a therapeutic intervention and follow-up of intervention outcomes and is critical for consistent interdisciplinary teamwork. In addition to allowing greater parental involvement during the assessment, the instrument is in line with US early childhood special education legislation (http://idea.ed.gov/) and is a valid and reliable measure of the child's abilities. kid.