In Mexico, the average income of men aged 25-30 with a full primary education differs by more than a factor of three between poorer municipalities and richer ones. The difference cannot possibly be related to educational quality, because those who moved from poor municipalities to richer ones also earned more.
各国的国内经验也同样发人深思。墨西哥25-30岁小学毕业男性的平均收入在穷市和富市相差3倍。造成上述差异的不可能是教育质量，因为那些从穷市迁移到富市的劳动力同样赚得更多。