This is a wonderful, simple role play for aggressive/assertive/passive responses to teasing which you might adapt or find a use for.  It's very simple.  It was created by a man named Bill Eyman who works with the Rhode Island Dept. of Ed:  his job is to create community in schools!  Anyway, the role play goes like this.
       First I model for the students three responses to teasing: aggressive, passive, and assertive.  I do this by pretending I am a kid and asking for a volunteer to tease me about my homework.  My aggressive response has an angry face and a clenched fist and my words put the teasing student down directly.  My passive response has a sad face, slumped body, and my words accept the teasing as "probably right," but then I move to student in the audience and talk about the teasing student in unfavorable terms, such as, "You know Jessica?  Well, don't you think she's not very nice?  I mean, you know, she's not any fun either, don't you think?"  This is the most complicated response because I'm trying to show the kids that talking behind someone's back is a way of not dealing w/ the person directly and it creates problems rather than solves them.  The assertive response has open arms signifying open heart and mind, eye contact w/ the teaser, and in my words I stand up for myself without putting the other person down: "I did the best I could on my homework and I'm proud of it.  If you think I could do better then next time why don't you help me?"  or something of the sort.  Then I circulate around the room and pretend to tease kids about homework and their job is to give an assertive response.  During this I do a lot of fine tuning because often kids will use assertive, respectful language with a hostile tone; I fine tune the tone and sometimes the words.  This is a great little role play and it can be done in about ten minutes; do it once a week in a classroom and you'll find kids gradually learning to be assertive.