This study compared the reading comprehension abilities of learning disabled (LD) students with the performance of both their age-peers and their reading-level peers. Subjects were 16 seventh- and eighth-grade LD students, 16 normal achieving eighth graders, and 16 normal achieving fifth graders. To assess the use of prior knowledge under varying conditions, reading passages included both familiar and unfamiliar topics. All passages tested inferential reading ability, since the answers to test questions could be inferred from content, but were not explicitly stated. Inferential tasks are most appropriate for use in reading research, since all reading tasks ultimately involve a search for meaning, and meaning is often implicit. Subject-activation and experimenter-activation of prior knowledge were also compared. Results indicated that all groups benefited from experimenter-activation of prior knowledge, but benefits were most noteworthy for LD subjects and when passage topics were unfamiliar. The LD subjects were strikingly similar in performance to their reading-level peers, as against their age-peers. (Six tables of data are included and 27 references are attached. Appendixes include 12 additional tables of results.) (Author/MG)