The structure of a textbook reflects is intended use in the classroom, with chapters of equal length to facilitate completion of the entire text in a single academic semester or year. The idea is to cover the field in a comprehensive manner, without going too deep in any particular section.
Textbooks set out clear learning objectives, usually at the beginning of every chapter. These objectives are often reinforced with testing materials at the end of every chapter, sometimes in a special dedicated website set up by the publisher for students to test themselves.
A good textbook will vary the pace and intensity of the information delivery by including several features to reinforce learning: sidebars with biographical information on key figures, time lines and, of course, illustrations.
Although a textbook is organized to provide a survey of a field, it should also provide significant resources for more advanced research. Bibliographies are essential and are often placed at the end of each chapter as well as at the end of the book.
Organized at the end of the textbook are several supporting resources. An index is essential, and often textbooks will include other elements such as pronunciation guides for foreign terms, a glossary, and so on.