A single science textbook often provides the syllabus for courses at upper secondary and tertiary levels, and may be used as a principal source of information or explanation. The research reported in this article challenges such practices. The ways in which the concept, acceleration, is treated in physics textbooks is compared with understandings of the concept demonstrated by final-year secondary (Year 12) and first-year university students. Some students' understandings are shown to be incomplete in ways that parallel misleading or inaccurate textbook treatments of the concept. In addition to misleading or inaccurate statements, the limitations of some textbook treatments of acceleration were found to include: lack of attempts to make explicit relationships with other concepts, failure to point out when it is appropriate to use particular definitions or that an alternative definition might be more appropriate in specific situations, inclusion of operational definitions without conceptual explanations, and a focus on quantitative treatments while overlooking the development of qualitative understanding. Two principal aspects that distinguished the ways in which the students understood acceleration were identified: (a) the relation between acceleration and velocity; and (b) the relation between acceleration and force(s). The results of the study have implications for teaching and, in particular, for the use of textbooks in teaching. These implications are discussed in the article.