A teacher usually has her own reasons to suggest a book to students. The book must be useful or it must cover some subjects that they are going to learn or there is a good view of something or it may be invaluable for collecting ideas, and so on. Most of the cases, the teacher does not require the students to read the whole book. In other words, some chapters or some pages relate to the subject they concerned or they discuss are recommended.
Many students, however, tend to read without the aim to a specific content when they start reading. They simply read the book and they generally read it from the beginning. Word by word, from line to line, this page and another are read for great details. It is plain that they do not organize the ideas that they have just read. They just follow the basic order of ideas that are shown in the book according to the intention of the author. Therefore, they have not a general overview of the aspects of the book. As the result, the students easily forget the knowledge they gain from that book.
Those are my own ideas about the way most students read books. Students in high-schools should be taught some techniques of reading. This will make them good habits of reading materials, especially text books.”