One of the functions of using computers is to manage pupils' performance in learning. This paper discusses a project from which pupils' errors in addition and subtraction of whole numbers from 3000 pupils were identified. Some errors were systematic and some errors were random. Different types of systematic errors made from addition and subtraction were identified. Based on these errors identified from pupils, a computer system was constructed which was able to store and retrieve them in a systematic manner. The computer system was able to identify pupils' systematic errors when they attempt to compute those problems which were generated by the computer system. The computer system can also identify whether the errors made were systematic or random and errors can be printed out for analysis. In this project a CD ROM would be developed and used for field-testing. The result will show the extent to which it can identify pupils' errors in addition and subtraction. In the presentation, the author will (1) show the research data obtained from 3000 pupils (2) demonstrate the computer system with the CD ROM and (3) some of the field-tested data for verification of the effectiveness of the computer system.