Enhancing students' critical thinking capabilities stands as the top goal of undergraduate education, according to faculty from many universities. We assessed the change in critical thinking skills with a sample of 176 students enrolled at either the University of Colorado Boulder (UCB) or Colorado College (CC) by employing the Critical-thinking Assessment Test (CAT) developed with collaboration and support from the National Science Foundation. Students' critical thinking progress was compared by assaying skills during the first and last weeks of the term in classes that expressly emphasized: (1) critical thinking, or (2) civic engagement, or (3) where, according to the class instructors, neither was a point of major emphasis. CAT scores improved significantly for students at both institutions, in different categories of class types, and over the dramatically different lengths of terms (3.5 weeks at CC vs 15 weeks at UCB). Our research contributes to an understanding of changes in critical thinking as part of the undergraduate experience. We demonstrate that the CAT instrument can be an effective tool for assessing critical thinking skills across very different institutions of higher education.