Prepositional phrases (PPs) are considered an important feature of mature written expression. However, little is known about the development of PPs during the school years. The study examined the use of PPs in 160 narrative and expository texts, written by Hebrew-users in grades 4, 7, and 11, and adults. PPs were identified, counted, and classified according to their syntactic roles. Statistical analyses were carried out to probe the effects of age and genre on the overall prevalence of PPs, and the prevalence of each role. Results show that PPs become more prevalent and functionally more diversified with age: PP prevalence increased significantly after grade 7 in both genres, and continued to rise after grade 11 in expositories. Grade 4 PPs had a limited set of roles, the majority serving as arguments. In the older age groups the proportion of arguments decreased, concomitantly with an increase in the prevalence of other roles--most markedly verb-adjuncts and noun-modifiers--and the emergence of new PP roles.