Despite a growing consensus among scholars and activists about the importance of religion, proposals for teaching about it have often been a source of division rather than unity in American public school districts. Faced with familiar cultural conflicts, Modesto, California, chose to become the first public school district in the USA to require all high school students to take an extended and independent course in world religions. The results of the first, large-scale empirical research on the effects of teaching about religion in USA public schools provides evidence that Modesto's bold approach was worth the risk. Surveys and interviews administered to students show statistically significant increases in students' knowledge about other religions, and levels of passive tolerance--willingness to refrain from discrimination--and active tolerance--willingness to act to counter discrimination. The course has not been the subject of lawsuits or complaints by parents and has gained acceptance among all of Modesto's religious groups. (Contains 1 table and 3 notes.)