Nursing schools face the challenge of producing graduates who are capable of providing safe patient care. Lack of adequate clinical practice focused on developing clinical judgment can place patients at risk. Instructional methods such as simulation and online learning may be ways to develop nursing students' critical thinking skills; however nursing research presently lacks sufficient evidence to support this. The purpose of this quantitative research study was to examine the effect of simulation and online case studies on nursing students' critical thinking skills and to compare these methods to lecture-only instruction in an associate degree nursing program. One hundred thirty-two third-semester associate degree nursing students in Chicago, Illinois were randomly assigned into one of three groups: simulation instruction group, online case study instruction group, and a control group that included lecture only instruction. The California Critical Thinking Skills Test (CCTST) Form 2000 was used to measure critical thinking skills before and after the treatment. Data were analyzed using analysis of variance (ANOVA) to test for significant differences among the three groups pre-test and post-test gain scores on the CCTST total score. The effect of group membership was statistically significant, F (2, 129) = 20.33, p < .01. Due to the potential non-normality of the distribution of gain scores, the nonparametric alternative to the one-way ANOVA (the Kruskal-Wallis test) was performed. This test also indicated that there was a statistically significant difference between the groups, χ² (2) = 32.19, p < .01. Thus, the null hypothesis was rejected and it was concluded that there was a difference between the simulation, online case study, and lecture group in terms of CCTST gain scores such that the simulation group was higher. Results from this study suggest instruction using simulation or online case studies is more effective in raising critical thinking skills than lecture only method. The recommendations for future research should include an increased sample size, extended research timeframe, and the inclusion of a qualitative component in the study design.