Aside from the discussions, this thread is worth linking to for its pointers to various studies like the one Baycas referred to i.e.,
"Evaluation of the effects of medium of instruction on the science learning of Hong Kong secondary students: Performance on the science achievement test, Bilingual Research Journal, Summer 2003 by Yip, Din Yan, Tsang, Wing Kwong, Cheung, Sin Pui."and the one cited by Inidoro i.e.,
"Mathematical Thinking and LearningAnother article worth mentioning is the one linked to by Manolo in his subsequent post i.e., Master English–but don’t neglect local languages article by the Business Mirror which cites a 1998 study by the ADB which concludes that:
2001, Vol. 3, No. 2&3, Pages 201-220
"The research by the World Bank and the Asian Development Bank (WB-ADB) in 1998 showed that the use of the mother tongue in the first years of school provides the necessary “bridge” for a child to learn a second language.
The WB-ADB study verified that children are less likely to drop out of school when classes are conducted in the home language. Pupils are active, not passive, in class recitation—and conceptualization, especially in mathematics, begins almost from the first day of school."