From the Introduction
Vocabulary knowledge is fundamental to reading comprehension; one cannot understand text without knowing what most of the words mean. A wealth of research has documented the strength of the relationship between vocabulary and comprehension. The proportion of difficult words in a text is the single most powerful predictor of text difficulty, and a reader's general vocabulary knowledge is the single best predictor of how well that reader can understand text (Anderson and Freebody 1981)
Increasing vocabulary knowledge is a basic part of the process of education, both as a means and as an end. Lack of adequate vocabulary knowledge is already an obvious and serious obstacle for many students, and their numbers can be expected to rise as an increasing proportion of them fall into categories considered educationally at risk. At the same time, advances in knowledge will create an ever larger pool of concepts and words that a person must master to be literate and employable.
The obviousness of the need and the strong relationship between vocabulary and comprehension invite a simplistic response: if we simply teach students more words, they will understand text better. However, not all vocabulary instruction increases reading comprehension. According to several studies, many widely used methods generally fail to increase comprehension (Mezynski 1983; Pearson and Gallagher 1983; Stahl and Fairbanks 1986).
Let me present the point in another way. Imagine an experiment with two groups of students about to read a selection from a textbook. One group is given typical instruction on the meanings of some difficult words from that selection; the other group receives no instruction. Both groups are then given the passage to read and are tested for comprehension. Do the students who received the vocabulary instruction do any better on the comprehension test? Very often they do not.
This news, if in fact it is news, should be unsettling. A major motivation for vocabulary instruction is to help students understand material they are about to read. If traditional instruction does not have this effect, teachers should know why not and what to do about it.
The purpose of this book is to lay out, on the basis of the best available research, how one can use vocabulary instruction most effectively to improve reading comprehension. The term "vocabulary" will be used primarily for "reading" vocabulary; the discussion will therefore be relevant primarily for students already past the initial stages of reading. For these students, learning new words means acquiring new meanings, not just learning to recognize in print words that are already part of their oral vocabulary. Although the focus is on improving reading comprehension, some connections will be made to other aspects of instruction, linking vocabulary instruction and to other aspects of instruction, linking vocabulary instruction and reading comprehension with broader goals of the language arts program.
Examples of useful approaches to vocabulary instruction -- mainly, but not exclusively, prereading activities -- will be presented for use or adaptation by classroom teachers. The primary purpose is not to provide a smorgasbord of activities, however. Rather, the purpose is to provide the teacher with a knowledge of how and why one can choose and adapt vocabulary-related activities to maximize their effectiveness.
