Test developers are continually exploring the possibilities Computer Based Assessment (CBA) offers the Mathematics domain. This paper describes the trial of the Place Value Assessment Tool (PVAT) and its online equivalent, the PVAT-O. Both tests were administered using a counterbalanced research design to 253 Year 3-6 students across nine classes at a primary school in Melbourne. The findings show while both forms are valid and comparable, the online mode was preferred by teachers. The affordances and constraints of using CBA in the formative assessment process are explored.