Any comparison of just white students in the US versus all of Finland is going to be misleading, in that it effectively allows the US disproportionately to ignore the performance of its economic underclass, while not allowing Finland to do the same.
Anyway, I have a theory that race is part of the reason our underclass underperforms so badly compared to many other countries. In the US, the political and economic elite tends to look very different, in an obvious and superficial way, from the lower class, and that makes it easier, psychologically, for the elite to write off those who are struggling. In a place like Finland (or, to a lesser extent, Massachusetts), when there is a group of people struggling for socio-economic reasons, there's a greater natural sympathy for them among the political and economic elite, since the underclass looks like their own family members. Thus, there's more focus on fixing the problems, whereas in a place with a racially differentiated underclass, the elite is more likely to just blame the victims and allow the problems to fester indefinitely.