Seventh-grade students were tested to uncover arithmetic errors. Answers and intermediate steps were analyzed and models to represent students' behavior were developed. Certain errors were common across students. Others were tied to the format of the test item. Some superficial understandings of mathematical concepts were exposed. (Author/DC)

A student was observed practicing arithmetic with a computer-assisted instruction (CAI) system. She enjoyed practice and believed that it helped. However, she consistently failed to solve problems on the computer that she could do with pencil and paper. This paper suggests reasons for her problems and draws implications for CAI. (Author/PK)