Estimation is more than a skill or an isolated topic. It is a thinking tool that needs to be emphasized during instruction so that students will learn to develop algorithmic procedures and meaning for fraction operations. For students to realize when fractions should be added, subtracted, multiplied, or divided, they need to develop a sense of size for various fraction quantities. They also need number sense, which will enable them to use estimation as a tool with fractions. When wrestling with quantities like three-fifths or nine-tenths, as individual fractions and in relation to each other, students will develop a sense of size and quantity for individual fractions. This experience is necessary if students are to develop meaning for fraction operations. This article explores the ways that estimation is used when students are learning to add, subtract, multiply, and divide fractions. (Contains 1 table and 2 figures.)