Clegg (2009: 46) issued that there has been a tendency that government in different parts of the world nowadays are interested in introducing English-medium teaching (bilingual education) into the school system. In Indonesian context, the attempts to teaching other subjects through English (TOSTE) or the use of English as the medium of instruction (MoI) have been widely tried to be implemented in the schools around the country, especially at International Standard School (ISS). The English mastery of other subjects’ teachers (OST) becomes one of the key factors on the success or failure on the development of the bilingual learners (BL) on the mastery of the subject matters learned at ISS. This article is aimed at giving a brief overview on the implementation of bilingual education (BE) at the ISS. This article finds that the implementation of TOSTE or the use of English as MoI at ISS has raised many problems due to the lack understanding of the society on ISS and the lack competency of English mastery of the OST itself.