Bias has many different meanings. Now, correct me if I'm mistaken, but in this context, I believe we are talking about bias as a difference between a measured value and a true value.
What is the true value in this case? Is it the counterfactual performance a person would have if their SES were not low? Would that be the "right" true value in all applications? Might it not be the case that, in some contexts, the "right" true value is the person's actual current ability level and not some counterfactual of how they would do in other circumstances that were perhaps more just and fair? For example, what if you are trying to give them the learning opportunity best suited to their actual current ability level, not trying to rank people and only give the top-ranked some special status or credential?
What is the true value in this case? Is it the counterfactual performance a person would have if their SES were not low? Would that be the "right" true value in all applications? Might it not be the case that, in some contexts, the "right" true value is the person's actual current ability level and not some counterfactual of how they would do in other circumstances that were perhaps more just and fair? For example, what if you are trying to give them the learning opportunity best suited to their actual current ability level, not trying to rank people and only give the top-ranked some special status or credential?