The ability to comprehend the gist and the main ideas of a passage are important textbook reading skills. Since research into children's ability to extract the central thoughts from prose has produced mixed findings, a study was undertaken to determine how skillful children are at comprehending the gist and the main ideas of a passage. To insure that the findings could be generalized to actual classroom reading behavior, the study was conducted in a naturalistic setting--83 third grade and 89 sixth grade students in their own classrooms read unaltered expository prose from existing textbooks. Main idea comprehension was assessed through a series of traditional reading comprehension measures. The results indicated that the students tended not to comprehend either the gist of an entire passage or its main ideas. The findings suggest that educators should continue to teach students how to comprehend main ideas, especially in content area reading materials. (FL)