Language acquisition in children, ages 6 to 10 years, and their linguistic competence with respect to complex aspects of English syntax, are studied. The nature of specific disparities between adult and child grammar are discussed, and the gradual reduction of these disparities as the children's knowledge of language increases is traced. In all, 36 children are tested by means of psycholinguistic experiments for knowledge of 8 complex syntactic structures; 5 of the structures prove to be acquired in sequence, revealing 5 developmental stages in syntax acquisition. Of particular interest is the regular order of acquisition of structures, accompanied by considerable variation in rate of acquisition. The range of ages at each linguistic stage is considerable. The children's exposure to written language as complex language inputs is examined in relation to linguistic development rate. Reading background and current reading activity are surveyed through interviews with both children and parents and through daily records of the children's reading (and listening) over a one-week period. Information is given on amount and complexity of independent reading and listening, background in children's literature, and recall and recognition of books. Lists of books read and named are included. A formula was developed and applied to 150 books and magazines reported to judge reading complexity levels. Methods are assesed, and relationships discussed. Results show a strong correlation between reading-exposure measures and language development. (Author/CK)