Some locations of mission schools have more crime than others. Some areas have fenced yards. In some areas travel after dark should be restricted. In other areas one should avoid large gatherings of local people. Missionary agencies typically have a time of orientation for new MK teachers and at that time they will discuss personal safety issues. You might also obtain travel books (Lonely Planet, Backpacker's Handbook) about the country to which you will be going. The US Department of State web site may have this information.