In this paper it is shown a comparability problem in Pisa results of some countries among years and among countries. This problem occurs because the school age of each country is not considered and because there is no rule for the application date of the test in relation to the school year of each country. The case of Brazil is analyzed with detail. There are analysis of some other countries too, among them Luxembourg and Chile, that together with Brazil, were pointed out as having the biggest evolution in performance since 2000. It is shown that this evolution of performance may not be real.
Pisa; Comparability; School age; Composition of students by grade; Proficiency
