This study reveals that children from the age of four to six years are unable to segment meaningful sentences into component words. The experiment investigated three hypotheses of performance on a word-learning task for beginning readers and prereaders. Readers and prereaders were taught five words as oral responses, each word paired with a nonsense figure. Analyses confirmed that context-dependent words (past tense verbs, prepositions, functors), took longer to learn than did context-free words (nouns, adjectives). However, providing a sentence context did not make it easier to learn either word class. Unlike readers, prereaders had substantial difficulty learning the words, particularly context-dependent words, because prereaders failed to recognize these words as units in their language. Results concerning the effectiveness of teaching beginning readers sight vocabulary words are discussed. (Author/MB)