Sentence patterns are often crucial to the degree of understanding a child derives from the printed page, and if he is to fully understand what he reads, he must be able to analyze the written language patterns in which the information is conveyed. This study analyzed selected passages from three grade 4 basal reader series to determine which transformational generative rules were used in the derivation of the sentences. Reading comprehension was tested by means of cloze tests. Transformations were grouped into five categories--embedding, conjoining, deletion, simple, and position shift. Findings indicated (1) that there is a high degree of similarity between the occurrence of different types of transformations in each of the three series and among the types of transformations that were most difficult across grade levels; (2) written language was generally more difficult when embedding and deletion transformations were present; (3) the difficulty of the majority of transformations (except deletion) correlated significantly with the difficulty of the sentence and passage; (4) the number of transformations per sentence was not a good indicator of sentence difficulty except for those added in the middle of the story; and (5) significant differences occurred when students were grouped by sex. Pedagogical implications are then considered. (HS)