Critical thinking and planning skills are vital to a successful global community. Lack of critical thinking skills among adolescents is a major concern. According to developmental theory, lack of exposure to logic during adolescence may account, in part, for poor thinking skills. Lack of training in formal logic is hypothesized to be one reason for poor thinking skills among US youth. To test this, 190 adolescents enrolled in a multicultural urban school were assigned to one of three conditions. All students were pre-tested using the Ravens Progressive Matrices Test (Raven, 1986), the Test of Logical Thinking (Tobin, 1984), a test designed for the study to measure understanding of formal logic and a Likert-type scale to assess self-perception of thinking. One group received instruction in logic. The second group received instruction from a critical thinking curriculum. The third group served as control, receiving standard subject一area instruction only. After over four months of instruction, all tests were re administered. Students instructed in logic performed significantly better on all measures than either of the other groups. This suggests formal logic instruction may improve adolescents thinking skills. This research, and its implications for curriculum and teacher education, are discussed.