With the rapid advances in computer technology during recent years, researchers have demonstrated the pivotal influences of computer-assisted diagnostic systems on student learning performance improvement. This research aims to develop a Diagnostic and Remedial Learning System (DRLS) for an algebra course in a Thai lower secondary school context based on an enhanced learning diagnosis model which employs a novel technique to preset weight of association concepts for each test item and the learning preference style of individual students to advise the students how to improve their learning performance. To evaluate the effectiveness of this innovative approach, an experiment has been conducted on an algebra course in a Thai secondary school. Pre- and post-test, questionnaire and interview data have revealed that the suggestions provided by the system could help the students improve their learning performance. (Contains 4 tables and 4 figures.)