Early childhood assessment is a field in transition. Dominated from its inception by psychometric models and measurement strategies used with older children and adults, it is only now beginning to forge a methodology that is unique to very young children. Much of the early work in infant assessment was directed at determining whether infant behavior could predict later child performance (Brooks-Gunn & Weinraub, 1983; Honzik, 1983). In Nancy Bayley's first monograph concerning mental development, she attempted to specify those infant behaviors that could be tied empirically to later mental functioning. She posed such questions as “What specific behavior precedes later mental achievements? To what extent are these later achievements dependent on the earlier? Can we predict later development from early behavior? How do individual growth rates compare with the norm for a group of infants? To what extent are these rates affected by environmental conditions?” (Bayley, 1933, p. 7). The instrument that she developed, which has been revised twice since its experimental versions (Bayley, 1969, 1993), was intended to answer these questions.

The Bayley Scales of Infant Development II (BSIDII; Bayley, 1993) are used primarily to sample the intellectual and motoric growth of infants and toddlers. The scales are most successful in sorting, categorizing, and ranking children according to demonstrable parameters of infant behavior.