小组合作学习是目前国内外广泛接受和认可的教学理论。目前，国内最常见的英语课堂互动活动方式就是课堂小组讨论。基于合作学习理论的小组讨论活动与传统教学相比有诸多优点。但是，开展小组讨论时，学生随意聊天，用中文讨论，保持缄默等消极现象还很普遍。本文关注课堂小组讨论参与者的两个内在因素:二语水平和性格因素，旨在探讨这二因素怎样影响高中生在英语课堂小组讨论中的有效参与度。结果发现，二语水平与小组活动参与水平存在显著相关，而个性因素只对低水平学生的参与行为产生显著影响。此调查有利于从小组活动参与者自身出发理解他们的参与行为，此外，对小组讨论行为四个纬度包括:情感、合作意识、自我监控、交际技巧的分析旨有利于启发老师从哪些方面提高学生的有效参与度。

Group discussion is one of the most popular teaching methods in Chinese EFL classroom. Despite many proved benefits, its implementation is not without problems. Passive participating behaviors such as chatting, talking in Chinese, and keeping silent etc. are common. To explore reasons behind, this paper draws attention to two variables of individual differences i.e. L2 proficiency and personality to find out to what degree and in what aspects those two factors may influence senior high students' group discussion participation.The result helps to explain students'negative behaviors in group discussion. The individual variation in all four dimensions of participation, namely affect, self-monitoring, cooperative awareness and communicative skills can also help teacher to find out where students need instruction to maximize efficacy of group discussion.