Vocabulary instruction helps students increase their personal vocabularies. It also helps students improve their ability to determine the meaning of new words. Research indicates that vocabulary knowledge is highly correlated with overall reading achievement (Davis, 1944, 1968; National Reading Panel, 2000).
"In the areas of Reading and Language Arts, vocabulary instruction is critical to the improvement of comprehension and written expression. In content areas such as Social Studies and Science, vocabulary instruction is central to the development of new conceptual frameworks and the understanding of increasingly more sophisticated ideas. In short, vocabulary is directly related to knowledge acquistion."
Blachowicz, Fisher, and Watts-Taffe, 2005