Many studies have shown children do better if they get a basic education in their own language. This is important because about 476 million of the world’s illiterate people speak minority languages and live in countries where children are mostly not taught in their mother tongue.

http://portal.unesco.org/education/en/ev.php-URL_ID=20280&URL_DO=DO_TOPIC&URL_SECTION=201.html

It is not surprising that pupils who do not have a good enough command of the appropriate Scandinavian language to benefit by specific subject teaching, do learn more facts when these are presented in their mother tongue. Available research on this subject confirms these conclusions.

http://www.nordbas.org/MotherTongue.action?lang=en

The basis for the possible attainment of the threshold level of secondlanguage competence seems to be the level attained in the mother tongue. Ifin an early stage of its development a minority child finds itself in a foreignlanguagelearning environment without contemporaneously receiving therequisite support in its mother tongue, the development of its skill in themother tongue will slow down or even cease, leaving the child without thebasis for learning the second language well enough to attain the thresholdlevel in it (1977, p28) (p233).

http://www.pacificlearning.com/articles/SplashResearch.pdf

Rahsia & Fadhilat Fatihah & Mu'Awizatain