A study investigated the development of vocabulary knowledge in elementary school children as a function of story reading for partially known and unknown words. Subjects, 43 fourth-grade low-middle to middle-class children from a rural elementary school in the southeastern United States, participated in a vocabulary checklist in which they provided definitions or sentences for words they knew (known words), and checked off words they did not know the meaning of but were familiar with (partial-knowledge words). Children then read stories containing some of these words. The remaining words served as a control. Vocabulary growth was gradual for both known and unknown words. Moreover, word factors rather than text factors were more important in the development of vocabulary knowledge. (Contains 35 references, 3 notes, and 2 tables of data.) (Author/RS)