International large-scale assessments (ILSAs) are attracting global attention, but examining reasons for this sharp increase in demand is an under-explored area. Drawing on key concepts in policy borrowing research, this chapter synthesizes key explanations why ILSAs are so attractive to policy makers. From a demand side perspective, ILSAs captivate countries by projecting as follows: (i) the comparative advantage of numbers over narratives, (ii) the quest for a credible source of information in an era marked by a surplus of evidence, (iii) the weak link between national curriculum and some ILSAs, and as (iv) transnational accreditation of public education. On the supply side, two brand-new developments are identified: (i) the preoccupation with linking test accountability to “education is in crisis” and (ii) new ILSA derivative tools that urge countries to reconsider partial and non-participation. In the age of ILSA expansion and test-based accountability, countries are saturated in a surplus of assessments; yet, the predominant policy advice remains singular, and countries are discouraged from alternative non-standardized paths for measuring learning.