In Kindergarten, children investigate that counting forwards is adding 1 each time, and counting backwards is taking away 1 each time (Early Counting and Grouping 7).
In Year 1, children begin to develop their understanding of number lines, explaining that a jump forwards is adding 1, and a jump backwards is subtracting 1. They have then already developed this understanding when they are ready to investigate representing addition and subtraction on number lines.
Addition and Subtraction are best taught at the same time so students are developing equal understanding and capacity in both. Teaching addition separate to or before subtraction may mean students will be better able to add than subtract in later years. It is important to always ensure that a student is at the same Level for both Addition and Subtraction.