In 2002 the language policy for teaching mathematics in Malaysia was changed from the national language Malay, to English, to be implemented from the beginning of 2003. This gave the curriculum developers and importantly the teachers just six months to prepare for this change. This small study investigated how after 18 months, 22 secondary teachers and 127 students were adapting to this change. Teachers were adapting but still needed crucial support in targeted professional development. They were still working hard to become competent in the use of mathematical English in the classroom. Students were starting to use English in their thinking about mathematics. It seemed that context and difficulty both played a role in whether the students were using English. It is suggested that opportune case studies of this nature are important to be completed on the few occasions that fundamental systems changes are implemented. (Contains 3 tables.)