Correlations between vocabulary size and life chances are as firm as any correlations in educational research. Of course, vocabulary isn’t perfectly correlated with knowledge. People with similar vocabulary sizes may vary significantly in their talent and in the depth of their understanding. Nonetheless, there’s no better index to accumulated knowledge and general competence than the size of a person’s vocabulary. Simply put: knowing more words makes you smarter.

It has been estimated that the vocabulary of English includes roughly one million words although many linguists regard that as a slight exaggeration. Webster's Third New International Dictionary, Unabridged, together with its 1993 Addenda Section, includes some 470,000 entries. The Oxford English Dictionary, Second Edition, reports that it includes a similar number. It is fair to say that most people get by very well with a vocabulary of about ten thousand words.

The term 'sight vocabulary' refers to the number of written words an individual can recognise 'on sight' ie without the need to serially decode their constituent graphemes. It is thought that the brain is capable of accommodating only about five thousand words and it is widely agreed that sight vocabulary is the basis of fluency in reading because it means that the reading process is not hindered by the need to repeatedly decode the vast numbers of identical graphemes. The Literacy Toolbox will vocalise any unfamiliar words so that extending sight vocabulary is one of its primary functions.

Everyone has both a receptive and an expressive vocabulary. Receptive vocabulary is the range of words which the individual understands. Expressive vocabulary is the range of words which an individual routinely uses in his or her routine interactions with others. The one-sided nature of radio and television has meant that receptive vocabulary would always be greater than expressive vocabulary although the increasing use of electronic means of two-way communication are likely to have a positive effect on expressive vocabulary.

All of the Literacy Toolbox exercises are designed to contribute significantly to the development of sight, receptive and expressive vocabulary and this is achieved primarily by perceptual rather than instructional means.