This article reports the observed behaviors and difficulties that 11 precalculus and calculus students exhibited in reading new passages from their mathematics textbooks. To gauge the "effectiveness" of these students' reading, we asked them to attempt straightforward mathematical tasks, based directly on what they had just read. The students had high ACT mathematics and high ACT reading comprehension test scores and exhibited much of the Constructively Responsive Reading of good readers as described in the reading comprehension research literature. However, they were not effective readers of their mathematics textbooks. We discuss some reasons for this that might not be easily discernible among the variety of task-working difficulties of less able students. Finally, we pose questions for future research and suggest some implications for teaching. (Contains 3 tables.)