In this study, a peer assessment system using the grid-based knowledge classification approach was developed to improve students' performance during computer skills training. To evaluate the effectiveness of the proposed approach, an experiment was conducted in a computer skills certification course. The participants were divided into three groups: one that learned with traditional instruction, one given the conventional peer-assessment system, and one using the proposed peer-assessment system. The results showed that the learning achievements of the students using the proposed system were significantly better than those of the other two groups. Therefore, integrating the knowledge engineering approach with the peer-assessment process can benefit students' learning, and help them attain computer skills certification. The dynamic peer assessment with knowledge classification approach is not only useful, but can also be repeatedly applied to different question sets of the certificate of computer software application.