If our brain structures were different (at least in so far as the organization or distribution of cells within the cranium and not the external measurement) then one would expect adopted children from places where brains are very different to perform differently then peers in new locations.

Yet I remember reading a study that showed that black children from Africa adopted by white parents in Germany performed at the same level as their peers. There have been other such studies with very similar conclusions.

It could also be that differences in academic performance (I'm assuming academic is the performance you were referring to in your comment) are not accurate metrics for identifying the effects of differential brain organization.

In scenarios like that, it's also difficult to control for the impact of different level of support for students in academic matters. For example, focused support for under-performing students compared to relatively relaxed support for students meeting expectations.

I could probably also see the impact of different psychological factors associated with being adopted by a family on a different continent being hard to control for.

My rambling brain confounded a few studies I had read.

My mistake. I was incorrect about the study being related to adoptions. It was actually something interesting that happened in Germany. I had read an environmental interpretation of the Eyferth Study: https://en.wikipedia.org/wiki/Eyferth_study