In all countries, schools are sampled, attempting to control for some variables. Around 5000 students, 160 schools in the US. Note that schools may/may not choose to participate, and the same with students. PISA has minimum standards for acceptance as sampled selection, in an attempt to avoid the obvious bias that countries would have an interest to produce in their samples.

http://nces.ed.gov/surveys/pisa/faq.asp

Given the optional sampling, and obvious incentives, I'm skeptical that this is particularly accurate, and an apples to apples comparison.

Also, h... (read more)