Most of the studies in the book (2009) were carried out in a highly developed English-speaking countries. Is the research therefore applicable to non-English speaking, non-Western countries?

Yes, it is indeed the case that many of the studies are from developed countries and generalizing to other countries needs much caution. Relative to high income countries, academic achievement in low-income countries can be more affected more by students’ social status and less by teacher quality. It is for this reason not recommended that this research is used in developing, non-western countries.