I was not an author of this thesis (Claudia Alvarez was the sole author). I am nevertheless including it on this site because 

The thesis presents an extensive meta-analysis of critical thinking skill gains over one semester among undergraduate students.  It provides what is to my knowledge the first rigorous estimate of the extent to which undergraduates' critical thinking skills actually improve in the course of undergraduate education - about 0.1 of a standard deviation over a semester. 

This constitutes a baseline against which to compare other approaches to inculcating critical thinking skills.  Of crucial importance for the Reason Project, the meta-analysis indicates that the Reason Method, properly deployed, can produce gains of around 0.8 SD.  Thus, it appears that the Reason Method, can improve students' critical thinking skills 8 times faster than "business as usual."