This study validated the Watson Glaser Critical Thinking Appraisal (WGCTA) on a sample of 273 private university students in Lebanon. For that purpose, evidence for construct validation was investigated through identifying the test's factor structure and subscale total correlations, in addition to differences in scores by gender, different levels, and streams using a series of ANOVA tests. Evidence for the test's reliability and concurrent validity was also collected. Moreover, students in five courses that emphasize critical thinking were pre-post tested using the WGCTA. Exploratory factor analysis revealed a unidimensional factor while results showed no significant differences in scores on the WGCTA between males and females or between students at different levels except for graduate students in the Business stream. Furthermore, results revealed significant differences for the senior students between different streams. Finally, results showed no statistically significant changes in the mean scores of students who were pre-and post-tested except for nursing students. The test's significant correlations with various criterion measures provided evidence of its convergent and divergent validities. The results were discussed in terms of the nature of the construct itself, and the effects of training and effective instructional strategies on growth of critical thinking. Recommendations for future research were proposed.