This article describes the results of a case study evaluating the influence of the intended (textbook) and implemented curricula’s (teachers’ instructional practice) adherence to the National Council of Teachers of Mathematics’ (NCTM) Standards on student outcomes in mathematics. We collected data on 72 third-grade students from four classrooms in one elementary school. Textbook and teacher adherence to the standards were evaluated using content analysis and direct observation procedures, respectively. Student achievement and attitude toward mathematics were measured through open-ended word problem solving tests and an attitude questionnaire. Results regarding the interactions among the intended, implemented, and learned curricula suggested that the textbook used in this school might have primarily influenced student achievement and attitude toward mathematics. Findings suggest that improving student outcomes may include not only changing instructional practices but also addressing changes in textbooks employed within instructional delivery.