On the right side, have them list people they know that don't have these stereotypes, then discuss why you can't generalize characteristics to certain groups.
2) Have students write of their personal experiences (themselves or with friends) with racism or discrimination. Have them not sign it, but hand it in, then have other students read them out loud and discuss them with the students. This will help the student reading it to learn empathy, as well as the students who discuss it.
3) Have the students then re-write the outcome of the incident to be positive, for constructive problem-solving and learning.
4) Ask students to write out what racism means to them (the definition). Discuss the definition afterwards: A generalization used to define a whole group of people based only on the words or actions of a single member of that group.
Give examples where you explain that being racist and generalizing is like saying "all blond people are stupid; all girls are poor in math; boys can't draw" etc.
5) Give students a project to go to the library and research FAMOUS people (eg politicians, doctors, actors, etc) of different cultures and to write an essay on the person (eg. Gandhi, Martin Luther King, Nelson Mandela). This will inspire them and show them that people of those cultures (including their friends) have the equal ability to reach great heights also.
7) If your school has people of mainly one ethnic, bring in an adult whose from a different background, once a week to help you teach or read to the students; familiarity with people of other cultures breeds understanding. Separation perpetrates myths. Just having that person around will acclimatize the students and that alone is valuable teaching.
8) Celebrate the ethnic holidays of the various students in your class and discuss what each holiday means. Make it fun, with food, costumes, etc., so that students learn what they have to learn from others is interesting and their lives are all the more richer for it.
9) Have video or film days, where you can show films or videos to students for an hour or so to teach them that way (eg. the documentary, "Roots", can be shown over a few days or weeks.
10) Have parent days where parents come in and discuss their jobs to students so that the students see that people of all cultures are productive and give to society
11) Discuss the images of various ethnic groups shown in movies and t.v. and how they're realistic or not (eg make comparisons to the real world). Also, discuss lyrics of various artists' songs.