I looked at the IB web page and it appears to be "critical thinking" as opposed to direct instruction in logic or other more-practical reasoning skills. The first problem is that there is lack of agreement about what critical thinking is (Lloyd and Bahr, 2010). Another problem is whether critical thinking skills are generalizable. What I know of critical thinking assessment is that there is emphasis on high-level approach to problems and a lack or complete absence of formal logic, math, statistics, or other specific skills that might help people to solve complex problems. There is no way that a class in critical thinking can substitute skills for logic, math, or statistics, but if it introduces topics that help kids advance to the next level, then it might be worth it. If teachers assert that people who complete the course "have good reasoning skills," then the class could be doing more harm than good.

Reference

Lloyd, M. and Bahr, N. (2010). Thinking Critically about Critical Thinking in Higher Education. International Journal for the Scholarship of Teaching and Learning. Vol. 4, No. 2 (July 2010)
http://academics.georgiasouthern.edu/ijsotl/v4n2/articles/PDFs/_LloydBahr.pdf