In this research monograph, several areas of disparity between child and adult grammar are examined to discover at what ages the child, who is on the border of adult language competence, achieves a certain mastery of complex syntactic structures. Chapters include (1) a discussion of current notions on the nature of the linguistic process and a hypothesis about the structures which children tend to acquire late in their development, (2) a description of an experiment to test the hypothesis--the 40 children used for the sample, interview procedures, and the design of test sentences which centered on the four complex structures of "easy to see,""promise,""ask/tell," and pronominalization, (3) an analysis of the grammar used in the children's responses to the test sentences and the nature of the structures they used (Portions of the actual interviews, photographs of subjects using test materials, and graphs comparing the children's responses are included.), (4) a correlation of the results from the four structures tested, and (5) such conclusions as the fact that the rate of a child's growing language performance cannot be predicted, but that the order of it can be. (JB)