Success in Numeracy Education (SINE) is the major numeracy approach being implemented in Victorian Catholic schools. SINE is designed to assist teachers to identify the mathematical understanding of the students they teach and to develop activities to help all students to progress at their relative level of understanding. Two components of SINE have been piloted and implemented: SINE Prep to Year 4 and SINE Years 5 and 6. This paper focuses on work with fractions being undertaken as part of the pilot program for SINE Years 5-8. There has been considerable research into the difficulties experienced by students learning fractions at all levels of schooling (see, for example Hunting, Davis and Pearn, 1996; Siemon and Stephens, 2001). In 2002, two forms of assessment were developed at the Catholic Education Office in Melbourne to determine the rational number knowledge of students from Years 5-8. Initially, a clinical interview was developed and subsequently two paper and pencil screening tests. The assessment instruments have been designed to probe the rational number knowledge of students in Years 5-8. In this paper, the process undertaken in the development of these three tests and the results from the initial trials are discussed. [Author abstract, ed]