East Malaysia is a relatively conservative place. Many of the communities on our project are in majority Muslim areas and you are likely to be working along Muslims in almost all placements. To become accepted into your communities and to avoid causing offence, please try to bring clothing that covers your shoulders, legs and chest (men and women alike). As the climate is generally hot and humid, try to bring light, long-sleeved, high-necked tops. Long skirts for women and light trousers for men are suitable for these communities. The cities are generally more liberal and you can be more relaxed (shorts, T-shirts etc) in areas where people are more used to seeing a mixed populations.
When working in schools and other education buildings (in any area, Muslim or not), you will need to dress conservatively as there is a Ministry of Education dress code which is very similar to the expectations on teachers in other counties, including the west. You cannot wear jeans or shorts in education buildings. Women should bring clothing that covers their legs, shoulders and chest. Men should bring shirts, ties and long trousers. Ties may not be needed in all schools but some do expect it. Suit jackets are not expected. Do bear in mind that schools are very rarely air-conditioned so aim for light cotton fabrics rather than polyester and be prepared to perspire!
One note: female teachers are expected to wear skirts (below the knee) in schools by the Ministry of Education. Trousers can only be worn if with an Indian-style long top (salwar kameez). This requirement does not extend to ELTDP mentors (as you are not employed directly by the MoE) but it would be very considerate and thoughtful to follow this rule and in very rare instances, local teachers have mentioned this to female mentors.