The FIRST question I pose to incoming students each year in my inner city high school Sociology class is: "In all your twelve years as a student in the Miami-Dade County Public Schools has anyone ever said anything GOOD about firearms, or BAD about the United Nations? Sure enough, nothing good about guns or bad about the UN.
I tell them they have been victims of an agenda and one of the major goals in class will be to learn to spot an agenda; anyone's agenda in moments. I also challenge them to look for my own agenda and to challenge it by checking facts (not opposing opinions) outside of the classroom.
I want them to make up their own minds based on their own values and not manipulated by outside forces be they parents, teachers, clergy or whatever. So far, it's a smashing success. I've been doing it fifteen years. Named Teacher of the Year in 2001 for my school.