We just need to compare with country of origin performance. If a family relocates from a place with low scores to a place with high scores, can you explain why you think we would expect their scores to rapidly increase to match the new place? I can think of many factors that would work against this that have nothing to do with race or genetics.

If the study is not controlled for this, then the education system at large may not have the kind of problem we would think about if we ignored this aspect. That seems pretty important to the discussion, I think?