After more than 20 years of lamentation, exhortation, and little improvement, writes the author, perhaps it is time to ask a fundamental question: Can critical thinking actually be taught? People who have sought to teach critical thinking have assumed that it is a skill, like riding a bicycle, and that, like other skills, once learned, it can be applied in any situation. Research from cognitive science indicates that thinking is not that sort of skill. The writer discusses the nature of critical thinking and explains why it so difficult both to do and to teach. Studies cited lead to three major conclusions: (1) Critical thinking (as well as scientific thinking and other domain-based thinking) is not a skill, but is context-dependent; (2) Certain metacognitive strategies may be learned that make critical thinking more likely; and (3) Ability to think critically depends on domain knowledge and practice. (Contains 2 notes, 20 endnotes, and 1 figure.) [This article is reprinted with permission from the Summer 2007 issue of the "American Educator.]