The purpose of this proposed quantitative, ex post facto, comparative study with a pretest-posttest design was to assess gains in overall Critical Thinking (CT) skills, and particularly in the Hypothetical-deductive Reasoning (HDR) skills, for pre-health college students tested before and after a Critical Analyses in Science course they attended in 2018 at a university in the southwest United States. The Constructivist Learning Theory (CLT) was used as a framework for this study. Archival data collected from N = 111 students at the beginning and at the end of the course using the Lawson Classroom Test of Scientific Reasoning (LCTSR) were analyzed to answer two research questions regarding the statistical significance of pretest-posttest differences in students' CT scale scores (measured with a two-tier CT scale and an Alternative "Individual" CT scale) and HDR subscale scores on the LCTSR. The results of paired-samples t-tests evaluated at corrected [alpha] = 0.0167 showed a statistically nonsignificant gain (pretest minus posttest) in two-tier CT scores, t(110) = -1.674, p = 0.048, Cohen's d = -0.159, a significant but small-size gain in Alternative CT scores, t(110) = -2.904, p = 0.002 < [alpha] = 0.0167, Cohen's d = -0.276, and a nonsignificant decrease from pretest to posttest in two-tier HDR scores, t(110) = 1.415, p = 0.160, Cohen's d = 0.738. The study confirmed previously identified problems with LCTSR, especially with the HDR scale, and the need for new validated instruments, possibly subject- or domain-specific, to measure student gains in CT skills in higher education. The study findings are relevant to curriculum development and faculty training. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]