Based on their scores on a proficiency test, the 894 participants in this study were grouped into three experimental groups (EG) and three control groups (CG). They attempted an argumentative writing task and the Cornell Critical Thinking Test, Form Z (CCTT-Form Z) as the pre-test. While CG participants received no treatment or placebo, EG participants received a three-week workshop treatment aimed at reconstructing their critical thinking and argumentation abilities. Two weeks after the workshop, all participants in all EG and CG groups attempted the same writing task and the Cornell Critical Thinking Test, Form Z (CCTT-Form Z) as the post test. SPANOVA analyses revealed that EFL writing performance will boost if EFL students' are helped to deconstruct, and then reconstruct, their cognitive and thought patterns for appropriate argumentation. The Multiple Trait Scoring Rubric for scoring students' writing (based on Hyland, 2003, p231) is appended.