The purposes of this investigation were: 1. To determine the minimum reading ability, expressed in grade equivalents, needed by 75 percent or more of the tenth grade student population to comprehend, at an independent level, their assigned English, social studies, and science textbooks which range in read ability from the tenth to twelfth grade level. 2. To determine the differences in the tenth grade students' comprehension test scores on tests developed from their textbooks in the areas of English, social studies, and science for each reading grade equivalent level from seven to thirteen. To determine the reading grade equivalents of the tenth grade students in the sample, the comprehension section of the Gates-MacGinitie Reading Test, Form E, was used.