This paper reports on a study conducted to determine the abilities of children to make optional transformations in sentences conjoined with "and." The subjects were 35 middle-class children between the ages of five and eight, who demonstrated average school achievement, spoke standard American English, and had normal speech and hearing. A repetition-of-sentence test, including 64 sentences each composed of two constituent transitive sentences conjoined with "and," was selected as the most efficient method of eliciting sentences representing specific structures. The main conclusions of the study are summarized as follows: (1) Children from 5 to 8 repeat or modify the structure of a dictated sentence on the basis of their grammatical competence; (2) Children's success in repeating a sentence depends on the specific transformations used in deriving the surface structure;(3) The ability of children to make deletions and substitutions progresses, in a general way, from 5 to 7 years and reaches a plateau between 7 and 8 years; (4) Children's acquisition of optional transformations on sentences conjoined with "and" proceeds in a sequence from deletions involving only the verb phrase, to deletions involving a combination of constituents from noun and verb phrase, to deletions or pronoun substitutions involving only the noun phrase. (Author/PMP)