The purpose of this article is to describe the assessment-driven instruction that facilitated third graders' increased understanding of informational texts, as revealed in their written responses to texts during one school year. The key instructional practices included making transparent for students what it means to synthesize, engaging students in interactive read-alouds, assessing students' written responses regularly, and using what was learned from the assessments to develop think-aloud minilessons. The article includes analysis of students' written responses throughout the school year. The authors reveal how the majority of the students grew in their ability to synthesize the ideas relevant to the overall meaning of the text and to develop their thinking using details from the text. (Contains 4 figures.)