Textbooks are required in most introductory college science courses, but students may not be benefitting from the textbooks as much as their instructors might hope. Word use in the textbooks may influence textbook effectiveness. I tested whether either the amount of technical vocabulary or the readability had a significant effect on students' ability to learn general biology concepts. I provided different versions of the same reading, then tested students on the content. On the topic with the lowest overall post-reading quiz scores, students who received readings with less technical vocabulary outperformed their peers (P = 0.03). Textbooks did not appear to be an important source of learning for students in this study; fewer than half the students reported that they were reading the assigned chapters near the start of the semester, and this number declined sharply. Students had difficulty correctly answering questions immediately after reading brief selections, indicating a low level of comprehension. Changes in textbooks and teaching strategies may improve student learning and reading compliance.