This investigation provides descriptive information about the developmental characteristics of syntactic and morphological structures found in the written Spanish language of native Spanish-speaking students in fourth to ninth grades. A sample population composed of 34 male and 56 female Spanish-speaking students was randomly selected from two Puerto Rican schools. Two stimulus pictures were chosen to elicit a 200-word writing sample. Twenty-one syntactic and morphological variables were chosen, and the degree to which they were associated with the students' grade levels was investigated. An analysis of the mean frequency scores of these variables based on their correlation with grade level showed those linguistic characteristics that concomitantly increased or decreased in length and complexity according to grades. Results of this investigation indicated that (1) the students wrote fewer clauses and T-units as they advanced in grade levels; (2) they increased the number of words in the remaining clauses by sentence-combining and sentence-embedding transformations; (3) they used more structure words than content words; (4) they de-emphasized the relative importance between clauses by converting more main clauses into subordinate clauses as their grade level increased. (Author/AMH)