The testing of English language learners (ELLs) is, to a large extent, a random process because of poor implementation and factors that are uncertain or beyond control. Yet current testing practices and policies appear to be based on deterministic views of language and linguistic groups and erroneous assumptions about the capacity of assessment systems to serve ELLs. The question "Who is given tests in what language by whom, when, and where?" provides a conceptual framework for examining testing as a communication process between assessment systems and ELLs. Probabilistic approaches based on generalizability theory--a psychometric theory of measurement error--allow examination of the extent to which assessment systems' inability to effectively communicate with ELLs affects the dependability of academic achievement measures. (Contains 3 tables and 5 notes.)