While the number line model is also an effective model for students as they represent and operate with fractions, it is tends to be a more difficult model for students as they initially learn how to work with these new numbers. The number line requires students to coordinate symbols and lengths in order to use the model which makes it a powerful but more sophisticated tool than area models like fraction circles and fraction bars. In our example, for a student to compute ⅔ + ¼ on a number line they would first need to decide how to correctly partition the number line before representing both fractions as one length. The planning needed for this decision is what makes using the number line a more sophisticated tool than working with area models. With area models both ⅔ + ¼ can be represented and combined before a student needs to decide to use a common size piece.

In general, students need substantial experience with various models as they make sense of fractions before they can begin operations like adding and subtracting. Students need to be able to estimate sums and differences using benchmarks which are supported by mental images before they carry out exact calculations. Area models like fraction circles help students develop number sense around fractions because they can visualize these numbers in relation to benchmarks like ½ and 1.