I think it would be fine to end high school at 16 as is done in Germany.

In Florida, a child can quit school at age 16 with the parents' permission. I don't know how many USA states have similar age thresholds. I'm guessing many do.

If you meant that Germany high school ends by default at age 16 for all students, then yes, the USA is radically different in that respect. Also, Germany's summer vacation is 6 weeks instead of USA's 12 weeks. Since Germany ranks ahead of USA in primary education standings, maybe they have the better system.

[1]http://statelaws.findlaw.com/florida-law/florida-compulsory-...

Correct me if I'm wrong, but doesn't school start when a kid is 6 years old in many parts of the US? If so, that might be part of the reason for the difference in school leaving age. For example, in the UK, schooling is only compulsory until the age of 16, but you start when you're 4. For higher (non-compulsory) education, the common path is two more years at a sixth form college, then three years at University.

Given the studies on things like Head Start, it seems unlikely that the effect of earlier school starts is this powerful.

I'm not familiar with Head Start, what is it?

Federally funded preschool.

I see. What do the kids learn at these preschools?

In the UK we have preschools for kids around 2 to 3 years old. They're mostly focused around play rather than formal lessons, but I think it helps kids to get used to a school-type environment and start to socialise with kids their age.

Here in The Netherlands you can either end high school at 16 and go to a trade school, end at 17 and go to a so called university of applied science (or higher professional education) or end at 18 and afterwards attend a research university. I really don't understand why Americans think that everyone should attend college, for most people that's just a waste of time which could be spent learning practical skills.