Cross-national comparisons of educational achievement rely upon each participating country collecting nationally representative data. While obtaining high response rates is a key part of reaching this goal, other potentially important factors may also be at play. This paper focuses on one such issue—exclusion rates—which has received relatively little attention in the academic literature. Using data from 20 years of international large-scale assessment data, we find there to be modest variation in exclusion rates across countries and that there has been a relatively small increase in exclusion rates in some over time. We also demonstrate how exclusion rates tend to be higher in studies of primary students than in studies of secondary students. Finally, while there seems to be little relationship between exclusion rates and response rates, there is a weak negative association between the level of exclusions and test performance. We conclude by discussing how information about exclusions—and other similar issues—might be more clearly communicated to nonspecialist audiences.