A considerable body of research exists on students' understanding of decimal fractions and the prevalence and persistence of common misconceptions related to this understanding. Results from major studies such as the National Assessment of Educational Progress (NAEP) in the United States and the Concepts in Secondary Mathematics and Science (CSMS) in Great Britain also indicated that decimals create great confusion for many students. A range of representational tools has been proposed to assist students as they develop understanding of decimal place value. In this article, the author describes an activity that helps students to make sense of decimal size and decimal place value and which encourages the use of fractional language to describe decimals. The activity involves the use of a Decimat, which is a proportional model for representing the size of decimal fractions and makes explicit the "ten-ness" of their base ten place value system. The Decimat was developed originally in New Zealand. An activity sheet is also included. (Contains 9 figures.)