Actually, this explanation does work pretty well for that also. Assume for the moment that Americans of European descent and Europeans have similar cultures.

Americans of European descent achieve test scores which are comparable to the top European nations + Australia.

http://super-economy.blogspot.com/2010/12/amazing-truth-abou...

The only reason the US as a whole does not fare as well as most European nations is because it's large proportion of non-Europeans drag the average down.

You get similar results when comparing Americans with Asian culture to Asians. Your culture explanation has a lot of explanatory power, and almost certainly more explanatory power than any explanation based on school system.

http://super-economy.blogspot.com/2011/01/how-well-do-above-...