International large-scale assessments (ILSAs) are an influential instrument for assessing and evaluating quality and equity across education systems and informing educational policies. The assessment of reading has been at the forefront in ILSAs not least because it is seen as one of the most important cultural techniques in our modern world. Caro and colleagues set out to tackle one of the biggest methodological challenges of ILSAs and describe how the studies’ design prevents research from drawing causal inferences due to bias that originates in a missing measure of prior attainment. Articles by D. L. Shepherd and J. O. Solheim and K. Lundetrae focus indeed on language and reading, although not necessarily underlying cognitive processes. Shepherd examines the effect of exposure to mother-tongue and English instruction on student reading performances in Botswana and South Africa. However, ILSAs have limitations by design and they accompany the scholarly work in each article of this special issue.