Critical thinking receives increasing emphasis from educators looking to infuse analytical thinking skills into the curriculum. Many research projects have been conducted on the transferability of critical thinking skills to other disciplines and how critical thinking may be taught. There are numerous studies on teaching critical thinking, yet none made use of a control group or attempted to evaluate ways in which students' critical thinking skills have improved. This study compares the effects of integrating critical thinking skills into a teacher preparation course in mathematics by examining a control and an experimental group. Results indicate that emphasis on critical thinking, even in one course content, can have positive effects on students' attitudes. Future work in this area should include measurable outcomes of other critical thinking skills with control groups. (Contains 4 tables.)