I have difficulties explaining negative numbers to my primary-level students. Thermometer scale is often used. Negative numbers is part of the Indonesian national curriculum.
Sinta, a teacher in Indonesia
I know that in some countries' curriculum, negative numbers are introduced in primary levels. In Singapore, we only introduced it at secondary level (grade seven). The number line strategy is suitable because it is visual. So thermometer or water level in a dam are suitable. With water dam analogy -2 can be described as 2 m below the land level. In that way we can explain why -2 + 1 = -1.