Abstract
The vocabulary size literature currently provides a rather pessimistic view of the role for direct instruction in increasing vocabulary size. A major reason for this pessimism revolves around estimates of the total number of words that individuals know and, hence, the number of words that would have to be taught in order to affect significantly normal vocabulary growth. When vocabulary size is expressed in terms of the number of functionally important words in the lexicon, however, estimates of vocabulary size are dramatically reduced. We adopted as a definition of functionally important words the list of main entries found in a moderate-sized, yet comprehensive dictionary of the English language. Using a dictionary-sampling method and multiple-choice testing of word knowledge, we estimated the lexicon size of junior-high students, college students, and older adults. The results lead us to suggest that there may yet be a role for direct instruction in affecting lexicon size of functionally important words.