To add or subtract using the number line, students simply have to count. The child starts at the initial integer and then counts to the right if adding or counts to the left if subtracting. Counting is one of the first math skills children learn, and by the time children are adding and subtracting, they've had a lot of practice counting. Because of this, using the number line is a simplified process.
Students can also interact with the number line in a tactile fashion. When counting to add or subtract numbers using the number line, children can use a finger, a pencil lead, or other object to follow the numbers along the number line until they reach the answer to their question. Children tend to be tactile when interacting with the world and learning. The number line facilitates this tendency.
Subtraction can be a difficult skill for children to learn. Learning to subtract negative numbers can be even more challenging. The number line provides children a way to visualize a difficult process. In the future, when children need to think about subtracting negative numbers, they only have to refer to the number line or visualize the number line in their heads.
When students first learn to add and subtract they will frequently be presented with a number line in their schoolbooks. Teachers may even have a large number line displayed in the classroom. However, students will not always have a number line available when they need one. Perhaps they will encounter a difficult math question later on in their academic career, or perhaps they will encounter a difficult math question in real life, and a copy of the number line is not available. As long as students have a writing implement and a piece of scratch paper, they can jot down a copy of the number line to help them solve the difficult problem.
Students also like the number line because the number line can be used to add and subtract numbers in a variety of situations. Students can use the number line to add or subtract regular math problems, understand fractions, calculate temperatures changes or add or subtract money.