By preschool, a child should possess the vocabulary necessary to be able to articulate her basic wants and needs. A child should know the words, for example, to be able to express the need to go to the bathroom. She should be able to express how she feels physically, such as whether she is hurt or feeling sick. She should be able to express her emotions adequately, such as being able to communicate if she is angry, sad or lonely.
A preschool child should possess the vocabulary necessary to take part in group classroom activities. For example, he should be able to take part in group singing and group reading, as well as be able to understand basic counting and colors. He should have the vocabulary to be able to interact with his peers, and be able to make requests for things, such as asking to play with a toy. He should know words necessary for basic social interactions, such as "please" and "thank you," and phrases such as "may I have."
Preschoolers should have the vocabulary to understand basic instructions from adults. Adults should strive to issue these instructions in easy-to-understand, two- or three-step commands, such as "take off your shoes, hang up your coat and sit on the mat." Preschoolers should understand command words and directions, such as "go to" or "bring."
To assess a preschooler's understanding of new, learned vocabulary words, the supervising adult must recognize the four steps of vocabulary understanding. The first step is when a child has no knowledge at all of a phrase or word. The second step is when she knows the word, but has no understanding of its meaning or use. The third step is having a fair knowledge of the word's meaning, perhaps only when the word is presented contextually. The fourth step is knowing the word and being able to remember it.