A study examined (1) relationships between background knowledge and reading passage comprehension, (2) the reliability of a passage-specific background knowledge measure used as the knowledge criterion, (3) the effect of a prereading language and concept organizer activity on available background knowledge, and (4) the effect of that prereading activity on responses to specific who, what, when, where, how, and why (wh) questions as well as on total comprehension. The subjects, 161 Long Island, New York, sixth grade students, were assigned to four prereading activities: prereading plan (PreP) group discussion of key concepts, motivation discussions of specific questions in small groups, no activity (reading without any preparatory discussion), and a distractor discussion of a nonrelated topic. Two passages from a social studies text were selected for reading, and students completed a 20-item test measuring wh comprehension. The results indicated that the background knowledge measure was a significant and reliable predictor of wh comprehension. The prereading activity significantly raised available background knowledge, and this in turn increased comprehension of moderately difficult passages. The measure of text specific background knowledge may be useful for teachers in assessing the difficulty of a reading assignment, and for researchers in controlling for differences in prior knowledge or in examining the relationships between background knowledge and various aspects of learning. (HTH)