Serving linguistically diverse populations poses a double educational challenge to countries. On one hand, substantial—and, in many cases, rapidly growing—numbers of students whose native language is not the language of instruction make it necessary for educational systems to have indicators of academic achievement based on which appropriate strategies can be devised to better serve them. On the other hand, the validity of such indicators can be compromised owing to the inevitable fact that testing depends heavily on the use of language (American Educational Research Association, American Psychological Association, & National Council on Measurement in Education, 1999).