If you didn't read that really carefully, go back and read it again. That is profound.
Within a fixed-performance perspective, people can be judged quite quickly. Indeed, people who take up fixed theorizing form stereotypes more quickly than those choosing dynamic theorizing, they are more inclined to apply trait thinking in describing group members, and they make more extreme trait judgments, whether positive or negative. In fact, people choosing fixed theorizing focus on information that confirms their stereotypes, ignoring disconfirming information. The more information goes against their stereotype, such as a poor, low-achieving boy doing well on a test, the less attention they give to that information. Within a fixed theory, once a student in judged as lazy (or friendly or learning disabled, etc.) we start to see evidence of it everywhere in their behavior. Their situation and psychological processes, such as intentions and feelings, take a back seat.
I wrote last year about a student that drove me buggy. It seems pretty clear to me that I had a fixed theory about that little girl and I was just lucky to be jarred out of it by the notes her kindergarten teacher had made on a form. I hope to be hyper-aware of this sort of thinking in the future.