The current study aimed at investigating the effect of the Master Thinker program on developing critical thinking skills of 11th grade students in Bahrain. Specifically, this research attempts to examine the hypothesis: Teaching the Master Thinker program will be significantly effective in developing critical thinking and its skills (inference, recognition of assumptions, deductions, interpretation, evaluation of arguments) of 11th grade students. A sample of fifty 11th graders from secondary schools in the Kingdom of Bahrain was randomly selected. The non equivalent control group design as a quasi experimental design was utilized. The Watson-Glaser Critical Thinking appraisal was administered to all study subjects before and after introducing the Master Thinker program to the experimental group subjects. Raven's Standard Progressive Matrices test was administered to both study group subjects at the beginning of the study as a covariate. One way Analysis of Covariance ANCOVA was used to test the hypothesis. The results revealed a significant effect on the gain scores of all critical thinking skills subtests (recognition of assumptions, interpretation, evaluating arguments, inference, deduction) favoring the experimental group.