Syntax in four published series of elementary school readers was analyzed to discover patterns of complexity increasing from first to sixth grade, to identify structures accounting for differences across the grades, and to compare the frequency of specific structures among the series. Analyses of 16 surface structures representing complexities derived from deep structure indicated an overall increase in syntactic complexities from first to sixth grade in all series. Patterns of increases were irregular, showing no evidence of systematic planning. A sharp increase in the number of total structures was found from first to second grade in the three series. There was a leveling off in the middle grades and another sharp increase from fifth grade to sixth. Significant differences among the series in the use of particular structures occurred most frequently in the middle grades. (Author/AA)