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MsEliza,

Many of our students go to voch/tech and apprentice type schools too.  Some drop out and join the military.  Some are incarcerated. Some just don't go to school. All too many are home-schooled.

It's the same story in many countries.  Our student pool isn't that much different than other countries pools to draw from.

Just because we teach to the test, doesn't mean there is no comparison, either.

Trendlines were emerging long before NCLB and teaching to the test.  Those trend showed us lagging behind.

What you're trying to justify won't automatically invalidate the comparisons in any case.

In most studies, if you look into the methodology used for any one comparison, there are analytical methods to control for variance.  Sampling weights etc.

And, in addition, looking further down the road, college testing bears out the same data.

And those comparisons come from within US colleges and Universities with foreign enrollments to draw from.

The same conclusions hold.