Although textbooks routinely include exercises to improve critical thinking skills, the effectiveness of these exercises has not been closely examined. Additionally, the connection between critical thinking skills and formal operational thought is also relatively understudied. In the study reported here, college students completed measures of formal operational thought (Group Assessment of Logical Thinking; GALT) and critical thinking skills (California Critical Thinking Skills Test; CCTST) both before and after completing four written assignments labeled in their textbook as "critical thinking" exercises. GALT and CCTST scores were significantly correlated at both assessment points, but declined over the course of the semester, suggesting that the critical thinking assignments did not have a positive effect on either formal operational thought or critical thinking skills.