A study determined if there would be any significant difference in comprehension from expository text between students instructed to use context clues and prior knowledge and those students not instructed in their use. It was hypothesized that students who only used a dictionary to understand words, not exploring context or prior knowledge, will not possess a true understanding of the word meaning. Subjects, 22 students heterogeneously grouped in a self-contained third-grade classroom, were divided into control and experimental groups. Subjects in the control group identified each unknown word, defined the words using a dictionary, and used the words in sentences. Subjects in the experimental group identified each unknown word using sentence context and activating existing prior knowledge about the word to gain understanding of the word. Results indicated that when students used a dictionary alone, they did not use the word in other reading and writing tasks more accurately than students who learned the meaning of words via context and relating sub-meaning to prior knowledge. (Contains 15 references and one table of data. Appendixes present test scores and word lists.) (Author/RS)