High school juniors and seniors participated in three studies of the effects of a thematic organizer on passage comprehension. Comprehension was measured using a cloze procedure in the first study and using a passage-reproduction task in the second and third studies. A thematic organizer (material presented to provide a context for the passage) was presented to the experimental groups before they read the passages; control groups were not given the thematic organizers. Inconsistent results were found between passages and between studies. This was interpreted as indicating that the type of material plays a major role in comprehension and in comprehension measures, limiting the generalizability of studies involving language samples. (Author/AA)