Assessment data and other research findings on fractions are briefly reviewed. These indicate that students are able to add and subtract fractions but have substantial difficulty finding and using common denominators. Selected results for nine-year-olds from the first and second national assessments of mathematics are used to portray what students can and cannot do. Implications for instruction are then noted: developing the concepts for fractions earlier, or reversing the sequence of fractions and decimals in the curriculum, is each suggested. (MNS)