This study investigated hearing-impaired students' understanding of the mathematical concept of fractional numbers, as measured by their ability to determine the order and equivalence of fractional numbers. Twenty-one students (ages 10-16) with hearing impairments were compared with 26 students with normal hearing. The study concluded that hearing-impaired subjects lagged behind their hearing peers in arithmetic computation and the development of the concept of fraction. The hearing-impaired students were capable of ordering the same types of fractions as younger hearing students. In general, they made the same kinds of errors as the younger hearing students, employed strategies in a similar way, and were negatively influenced by the size of the counting numbers composing the fractions. Possible explanations for this developmental delay are explored, and implications are discussed. A copy of the assessment instrument is included in an appendix. (Contains 26 references.) (JDD)