In Kindergarten I have definitely seen it shown Black kids do better with White teachers. Also seen the cheating scandals. It's really about the quality of the kids. I'd guess though if you took kids and teachers of each race with the same IQ/behavior you would get better results with someone who looks like you, as humans are designed to be around people who look like them, less stressful. Of course, IQs and behaviours aren't the same in almost all instances, so...