I think the problem with that analysis of the problem is that education spending in the US is highly unequal. Some school districts spend much more than necessary, while some don't have the funding to afford textbooks or safe school buildings. The main cause of this is that schools are funded by local property taxes, which depend on local house values and local incomes. Poor areas can't afford good schools, which makes it harder for kids raised in those areas to escape from poverty. Consider the Corridor of Shame: http://projects.aljazeera.com/2014/south-carolina-schools/
It may well be the case that US aggregate education spending is plenty high – but unless it were centrally collected and equitably distributed (taking into account differences in cost of living, cost of real-estate, etc.) to produce equivalent average outcomes, that's not really relevant.