In this paper, we present a mathematical model for forming heterogeneous groups of learners under different teaching strategies. This model requires a formulation which can effectively predict the learning performance of cooperative learning groups. Therefore, we explore the correlations between learning performance and various learner characteristics including learning motivation, learning strategy use, learning styles and gender based on real-world data. By means of analyzing learner data of 157 students in a cooperative learning course, learner attributes irrelevant to cooperative learning performance are excluded from the formulation; this sharply decreases the workload of group formation calculation. In future work, a tool will be implemented based on this adjustable mathematical model and this tool will be used in daily teaching to evaluate its effectiveness.