It think it varies widely across the country - based on how multicultural the area is. I guess most of the school deal with racial issues pretty well. But the problems comes in much finer grains that cannot be labeled as "racial issues". They are mainly cultural issues. One of my friends moved from India to Indianapolis. Even though his 6 years old daughter was very fluent in English from India, but still her accent and the English styles were different from Americans. Even though teachers understood her, but her classmates did not. Kids are frank and honest enough to tell her that she "talks weird" or "talks funny". She had to go through some isolation for some period. And sometimes it's painful. But the good thing is that children adapt more easily than adults. Another friend moved from Jackson, MS to Chicago for same reason. I live in San Francisco bay area and haven't heard this kind of issues. But in some schools I heard exactly reverse scenario. For example, single blonde girl was isolated among all Indian, Chinease children.
My wife is a teacher. She tell that surprisingly children are in general color blinds and they don't understand or try to distingush between black, brown, yellow or white skin colors. Most of time problem starts from home. If a child made a racial comment, most probably he/she learned from one of his/her peers or most likely from home (family members). If I am watching TV and keep discussing about "brown skin", "white guy", "ketchup-head" or "fat lady" in front of my children I should expect that my children will do the same in school. That's why most of the times this kind of issues eventually result summoning their parents.
From my experience I have noticed that parents who talk to their children in regular basis in friendly way get to know this kind of issues pretty fast - probably not in the form of complains but as honest confessions.
Being cold or unfriendly are human natures. I would not call it racial issues (unless I read their heads and find the root cause).