A study made to examine the development in production of the English verbal auxiliary and copula (VAC) "to be" compared a group of children with language dysfunction and a group of normal children. Two purposes were to see whether developmental differences are qualitative or quantitative and to calculate the importance of the VAC in language acquisition. Fifteen normal children (mean age 2 years 4 months) and 15 language-deviant children (mean age 6 years 7 months) were selected, and language samples were taken from each. Use of a form of the verb "to be" was charted for each group at each of five levels of language development. Results indicate that the difference between normal and deviant development of the verb is quantitative rather than qualitative, and suggest that deviance results from faculty performance rather than lack of competence. The data provide information important for language rehabilitation and therapy. (CK)