The author examined the effectiveness of a vocabulary intervention that employed structured, supplemental story read-alouds and related oral-language activities. Within each of 7 Title I schools across 2 sites, 15 third-grade teachers were randomly assigned to either use the intervention (treatment condition) or continue their usual practice (control condition). Trained test examiners administered oral and sight vocabulary pre- and posttests and reading achievement posttests. At 1 site, students in treatment, compared with control, classrooms performed significantly higher in vocabulary and reading achievement. In the other site, the intervention was not more effective. Contextual factors and student characteristics appeared to affect the results. (Contains 4 tables, 4 figures and 4 notes.)