It was poor wording on my part when I wrote "the contexts under which the adjustment was made". The spirit of my point is much better captured by the word "applied" (vs. made). That is, it looks like a balanced reading of stereotype literature shows that people are quite good in their judgments of when to apply a stereotype. My point is therefore a bit more extreme than it might have appeared.

I would think that many sociologists would say that many people who are racist and look down on Blacks are racists because they don't interact much with Blacks.

I agree with this and would add that such perceptions of superiority could be amplified by other members of the community reinforcing those judgments.

If the adjustment was made during a time where the person was at an all-White school, the interesting question isn't whether the adjustment performs well within the context of the all-White school but whether it also performs well at decisions made later outside of that heterogeneous environment.

To get a little deeper into this topic, I should mention that our stereotypes are conditional and, therefore, much of the performance of a stereotype depends on applying it in the proper contexts. Of the studies looking at when people apply stereotypes, they tend to show that they are used as a last resort under conditions in which almost no other information about the target is available. We're surprisingly good at knowing when a stereotype is applicable and seem to have little trouble spontaneously eschewing them when other, more diagnostic information is available.

My off-the-cuff hypothesis about students from an all-white school would be that they would show racial preferences when, say, only shown a picture of a black person. However, ask these students to provide judgments after a 5-minute conversation with a black person or after reviewing a resume (i.e., after giving them loads and loads of information) and race effects will become nearly or entirely undetectable. I don't know of any studies looking at this exactly and urge you to take my hypothesis with a grain of salt, but my larger point is this: You might be surprised.