Abstract: Within the content of a mathematics reform effort to implement algebra in elementary schools, there is pressure to provide results in the form of student achievement scores. However, widely used measures of student achievement may be unrelated to the ideas and instructional practices encouraged by the professional development program. The inappropriate use of student achievement scores often leads to inaccurate inferences about the quality of instruction. This study explores the validity of inferences about instructional quality using two measures of mathematics achievement: a measure of algebraic reasoning designed to closely relate to instructional activities and a measure of grade-level specific California content standards. This exploration includes multiple measures of classroom instruction to evaluate the instructional sensitivity of multiple measures of math achievement and applies an analytic method that makes it possible to relate student-level outcomes to teacher-level measures of instruction. Findings suggest that particular items measuring equality and relational thinking from the measure of algebraic reasoning were sensitive to instruction. In addition, the instructional opportunity variable related to performance for third graders (teacher awareness of students’ relational thinking strategies) was not related to performance for fourth and fifth graders. Thus, the ability of these measures to determine the impact of instruction on student performance depends on grade level, variables that define instructional opportunities, and the characteristics of the student assessment items. These factors should be considered when evaluating the relationship between instructional quality and student performance. Instructional sensitivity provides a framework to interpret student performance by creating a link between instructional opportunities and performance on particular assessment items.