A word about vocabulary from Jim Trelease, author of The Read-Aloud Handbook:

“There is one pre-kindergarten skill that matters above all others, because it is the prime predictor of school success or failure:  the child’s vocabulary upon entering school.  Yes, the child goes to school to learn new words, but the words he or she already knows determine how much of what the teacher says will be understood.  And since most instruction the first four years is oral, the child who has the largest vocabulary will understand the most, while the child with the smallest vocabulary will grasp the least.

Most conversation is plain and simple, whether it’s between two adults or with children.  It consists of the five thousand words we use all the time, called the Basic Lexicon.  Then there are another five thousand words we use in conversation less often.  Together these ten thousand words are called the Common Lexicon.  Beyond the ten thousand mark are the “rare words,” and these play a critical role in reading.  The eventual strength of our vocabulary is determined not by the ten thousand common words but by how many “rare words” we understand.  If we don’t use these rare words very often in conversation, where do we find them?  An adult uses only nine rare words (per thousand) when talking with a three-year old.  There are three times as many in a children’s book and more than seven times as many in a newspaper.