The problems of standard psychological tests
There is no single test that will serve to answer the question of whether or not a bilingual child has a learning difficulty. The process needs to be an evidence-based holistic approach where information is gathered from a number of sources.
Cultural bias – standardised tests embody the Anglo-centric conformity, by assuming that everyone is a member of a homogenous cultural and statistical population. We live in a pluralistic society and many ethnic and linguistic minorities have been exposed to very different learning experiences from middle-class English children. Tests are inevitably based on the culture of the dominant group; even tests for young pre-school children can make assumptions about the familiarity of play objects and experiences without necessary awareness of cultural differences.
Language bias – verbal tests are especially prone to bias and it is virtually impossible to design a verbal test that is appropriate for bilingual children. Even something as apparently simple as word association is fraught with difficulty because it depends upon familiarity with the context and the content of the problem.
Translation – translating tests makes them invalid due to issues around syntax and vocabulary.