Scone, you have a point about schools - but it depends on where you live. Schools in the US are funded predominantly by local taxes - a well-off suburb usually offers a great education, often with extras (labs, playing fields, arts) that rival a top prep school.
The opposite is true for children in a rundown rural area or, say, a city like Detroit.
Also, most states & school districts set their own curriculums and graduation standards (despite the minor impact of recent federal legislation).
This is why American teenagers applying to university have to take private exams - either SATs or ACTs. Because a straight-A average in one school district can equate to a B- or C-average elsewhere!