In this study, a peer assessment-based game development approach is proposed for improving students' learning achievements, motivations and problem-solving skills. An experiment has been conducted to evaluate the effectiveness of the proposed approach in a science course at an elementary school. A total of 167 sixth graders participated in the experiment, 82 of whom were assigned to the experimental group and learned with the peer assessment-based game development approach, while 85 students were in the control group and learned with the conventional game development approach. From the empirical results, it was found that the proposed approach could effectively promote students' learning achievement, learning motivation, problem-solving skills, as well as their perceptions of the use of educational computer games. Moreover, it was found from the open-ended questions that most of the students perceived peer assessment-based game development as an effective learning strategy that helped them improve their deep learning status in terms of "in-depth thinking," "creativity," and "motivation."