This project examined the words selected for instruction from fourth-grade English/Language Arts (ELA) and science programs with the goal of describing the unique words in these two text types. Seven features of the words were established: (a) length, (b) frequency, (c) frequency of a word's morphological family, (d) familiarity, (e) dispersion (i.e., how frequently a word appears across subject areas), (f) conceptual complexity, and (g) semantic relatedness. Analyses showed differences on all features except for the frequency of morphological families and dispersion. Narrative vocabulary was more familiar but less frequent than science vocabulary, but science words were longer, more conceptually complex, and more semantically related than narrative words. These differences lend themselves to different instructional approaches. In science, where unique words are conceptually complex, students benefit from extensive discussion and demonstrations. Because the unique words of narrative texts represent fairly familiar concepts, instruction should emphasize the ways in which authors vary their language. (Contains 4 tables and 2 figures.) [This document was published by TextProject, Inc.]