Building proficiency with fraction arithmetic poses a consistent challenge for students with learning difficulties or disabilities in mathematics. This article illustrates how teachers can use the number line model to support struggling learners in making sense of fraction arithmetic. Number lines are a powerful tool that can be used to help students represent and solve problems involving addition, subtraction, multiplication, and division with fractions while building conceptual understanding of the underlying operations. Evidence-based strategies for using number line models to teach fraction arithmetic concepts and skills are described and specific examples provided to illustrate how teachers can strategically integrate number line models with other mathematical representations to support the development of flexible understanding of fractions.