Links between international large-scale assessment (ILSA) methodologies, international organization (IO) ideologies, and education policies are not well understood. Framed by statistical constructivism, this article describes two interrelated phenomena. First, OECD/PISA and UNESCO/TERCE documents show how IOs’ doctrines about the value of education, based on either Human Capital Theory or Human Rights, shape the design of the ILSAs they support. Second, quantitative analyses for four Latin American countries show that differently designed ILSAs disagree on the effectiveness of a specific policy, namely, grade retention: PISA’s achievement gap between repeaters and nonrepeaters doubles TERCE’s. This matters and warrants further research: divergent empirical results could potentially incentivize different education policies, reinforce IOs’ initial policy biases and provide perverse incentives for countries to modulate retention rates or join an ILSA on spurious motivations. In summary, ILSA designs, shaped by IOs’ educational doctrines, yield different data, potentially inspiring divergent global policy directives and national decisions.