We estimated the invariance of educational achievement (EA) and learning attitudes (LA) measures across nations. A multi-group confirmatory factor analysis was used to estimate the invariance of educational achievement and learning attitudes across 55 nations (Programme for International Student Assessment [PISA] 2006 data, N = 354,203). The constructs had the same meaning (factor loadings) but different scales (intercepts). Our conclusion is that comparisons of the relationships between educational achievement and learning attitudes across countries need to take into consideration two sources of variability: individual differences of students and group differences of educational systems. The lack of scalar invariance in EA and LA measures means that the relationships between EA and LA may have a different meaning at the level of nations and at the student level within countries. In other words, as PISA measures are not invariant in scalar sense, the comparisons across countries with nationally aggregated scores are not justified. (Contains 2 figures and 5 tables.)