Numerous scholars have applied conceptual graphs for explanatory purposes. This study devised the Remedial-Instruction Decisive path (RID path) algorithm for diagnosing individual student learning situation. This study focuses on conceptual graphs. According to the concepts learned by students and the weight values of relations among these concepts, this study established the remedial-instruction paths to identify their real missing concepts. This study applies diagnostic and remedial learning strategies to two courses Introduction and Implementation of RS-232 and Electronic Circuits Laboratory. By analysing the scores of the midterm and final exams, evaluations of remedial learning yield positive experimental results. Participants who adopt the diagnostic and remedial learning strategy have better academic performance.