The purpose of this study was to investigate the effects and social validity of Read STOP Write, a text structure intervention for reading and writing, in grades four and five. In a cluster randomized trial, 11 teachers in three elementary schools were randomly assigned to deliver Read STOP Write or RARE Reading & Writing, an alternative treatment focused on question answering. In total, 160 students received Read STOP Write, and 191 students received RARE Reading & Writing. Data included pretest and posttest measures of students' informational text structure identification, reading comprehension, and writing quality, and interviews to understand teachers' perceptions of the social validity of the interventions. Student measures were analyzed using three-level hierarchical linear modeling. Teacher interviews were analyzed qualitatively using typological analysis. Results indicated that students who received Read STOP Write outperformed students who received RARE Reading & Writing on a researcher-developed measure of informational writing quality with promising effects on measures of informational text structure identification and reading comprehension skills but no effects on standardized measures of general reading comprehension or writing quality. Teacher interviews revealed that teachers perceived the goals, procedures, and effects of both interventions as socially valid. Implications for research and practice are discussed.