The students tested by PISA are aged between 15 years and 3 months and 16 years and 2 months at the beginning of the assessment period. The school year pupils are in is not taken into consideration. Only students at school are tested, not home-schoolers. In PISA 2006 several countries will however also use a grade based sample of students. This will make it possible also to study how age and school year interact.
Each student takes a two-hour handwritten test. Part of the test is multiple-choice and part involves fuller answers. In total there are six and a half hours of assessment material, but each student is not tested on all the parts. Participating students also answer a questionnaire on their background including learning habits, motivation and family. School directors also fill in a questionnaire describing school demographics, funding etc.