This study set to investigate the critical importance of integrating Student Team Achievement Division (STAD) and "WebQuest," STADIBTM for short, on developing the advanced-level argumentative writing skills of L2 English university students. The study employed a pre-posttest comparison of the experimental group (N=54) versus the control group (N=24). The data from the study have been systematically reanalysed to evaluate in detail how the initial learner proficiency levels correlated with improvements in the specific areas covered by the evaluation rubric that guided the collaborative writing activities of experimental group students.