Construction of a text microstructure is affected by the number of different arguments that must be activated and maintained in working memory, the number of propositions that must be formed, and the hierarchical arrangement of the propositions. Previous research has shown no developmental differences as a function of the latter two factors. This study shows that there are, however, developmental differences in the effect of number of different arguments. Fourth and sixth graders of high and average reading ability read and immediately recalled 24 paragraphs, half containing few and half many different arguments, from three content areas: history, science, and familiar experiences such as birthday parties. The difference between many- and few-different-argument passages in reading time per proposition recalled was significantly greater for fourth than for sixth graders. The pattern of results suggests that the effect is due to developmental differences in working memory that affect the overall retrievability of the microstructure but not how it is hierarchically organized.