A study tested the effects of hedges (which signal writers' tentative assessment of referential information) on readers' learning. Subjects, 145 ninth-grade students from three middle class junior high schools in a midwestern city who were ranked on the Iowa Test of Basic Skills, participated in the experiment--74 were randomly assigned to an experimental group and 71 to a control group. The text materials consisted of two passages of approximately l,000 words written at a ninth-grade readability level taken from two textbooks, one from science and one from history. The hedges appeared in either personal or impersonal voice; in either the first half, second half or both halves of the passages; and in either a low intensity condition or a high intensity condition. A measure of what subjects learned from reading the passages showed that they learned most when the hedges appeared in personal voice, in the second half of a passage, and in low intensity. Findings suggest that the implications of this work can be extended to practices in composition classes--particularly practices of evaluating whether or not material should be hedged--in order to broaden students' critical-thinking abilities and their views of language. (Two tables of data are included, and 66 references are attached.) (NH)