What a terrific subject. My experience is working many years with adults and children with developmental disabilities. Although it is very specific sort of disability I think the barriers are similar. There are many emotions that create barriers in becoming friends with kids that have any sort of disability. Children have a deep fear of the unknown and they look to their parents to vaildate their emotions. If parents act afraid or avoidant of people with disabilities often time children will mimic these emotions.
I think a parallel discussion is one of prejudice, especially in the conquoring and finding of a solution to break down such barriers. It is human nature to make asumptions about people as an innate survival tactic. Human nature hates the unknown. It creates anxiety, especially in children since so much of the workd is unknown to them because they have so few expereiences on which to base their knowledge.
Intergroup heterogeneity and outergroup homogenaity is a fancy way of saying that we see people like us as diverse and different, and we group "everybody else" is exactly the same. We like to explore people in our own groups because we can identify ourselves in them. It takes an outside force to motivate us to diversify the groups that we see as "everybody else".
As with prejudice, the solution to create harmony and real, not superficial friendships is through positive contact and declaration of similar goals. Kids with disabilities need to interact with all other kids. The kids need to realize they all have similar goals, hopes and aspirations. That is how you break down the barriers and create real friendships.




