In recent years, students in programming courses have shown a widening gap in learning achievement. Students often lack confidence and have difficulty learning. This paper developed a diagnostic method for assessing student learning in a programming course to help students and teachers identify deficiencies in the learning progress. The analysis results show the prior knowledge required for students to develop programming skill. It also shows the optimal learning path for all students in the programming course. Diagnostic assessment support enables teachers to modify the teaching method and reorganize the learning material. This paper showed that the proposed method supports students by increasing learning motivation and identifying blind spots in learning.