The positive effects of computer-supported collaborative learning (CSCL) on students' learning outcomes and processes have been widely reported in individual empirical studies and meta-analyses. More specifically, in the meta-analysis by Chen, Wang, Kirschner, and Tsai (2018), the effects were found to be attributed to the three main elements of CSCL including collaborative learning, computer use, extra learning environments/tools or extra supporting strategies. This study extends that meta-analysis by examining the moderating effects of educational level and subject area on the effectiveness of CSCL. The moderating effects of educational level were found not to be significant on the effectiveness of collaborative learning, computer use, extra learning environments or tools, or extra supporting strategies with respect to student knowledge achievement. Subject area, on the other hand, was found to be a significant moderator for the effectiveness of extra learning environments or tools and extra supporting strategies. When using extra learning environments or tools for CSCL, larger effect sizes were found for engineering and science courses; when using extra supporting strategies for CSCL, larger effect sizes were found for science and social science courses. The results also showed that more studies were conducted at the university level and in engineering, science, and social science disciplines.