Eight sixth-grade students received individualized instruction on the addition and subtraction of fractions in a one-to-one setting for 6 weeks. Instruction was specifically designed to build upon the student's prior knowledge of fractions. It was determined that all students possessed a rich store of prior knowledge about parts of wholes in real world situations based upon whole numbers. Students related fraction symbols and procedures to prior knowledge in ways that were meaningful to them; however, there was a danger of this prior knowledge interfering when it reflected algorithmic procedures rather than fraction ideas in real world situations. (Author/PK)