This study investigated the relationship between instructional use of handheld graphing calculators and student achievement in Algebra 1. Three end-of-course test forms were administered (without calculators) using matrix sampling to 458 high-school students in two suburban school districts in Oregon and Kansas. Test questions on two forms were drawn from Texas and Massachusetts publicly-released standardized test items, and the third form was custom-designed to emphasize conceptual understanding and math applications. All classes used Key Curriculum Press's "Discovering Algebra" textbook. Results showed that the more access students had graphing calculators, and the more instructional time in which graphing calculators were used, the higher the test scores. In addition, scores were significantly higher where teachers reported receiving professional development on how to use a graphing calculator in math instruction. Appended are: (1) Teacher Survey; (2) Classroom Survey; (3) End-of-Course Algebra Test Form T; (4) End-of-Course Algebra Test Form M; and (5) End-of-Course Algebra Test Form C. (Contains 19 tables.) [This work was also funded by Key Curriculum Press.]