Competition has been prevalent in all types of childhood activities including playing, learning, and living. Studies have shown that a well-designed competitive activity can motivate students to perform at an increased level. However, there have been few research studies on the relationship between learners' preferences and performance in relation to the level of competition in activities, especially in a computer-assisted learning environment. In this study, different levels of group and individual competitions were designed and implemented through an innovative multiple-mice learning system. Sixty 7th grade students were involved to interact with their own group members and compete with other groups to complete English vocabulary tasks. The preferences of students, of different levels of achievement, toward various competition activities were investigated upon finishing the tasks. This paper presents the potential of integrating the multiple-mice learning system into English learning tasks, and most importantly, it reveals the preferences of students regarding activities at various levels of competition in a computer-assisted learning environment.