Assessment policy internationally places significant importance on the use of assessment criteria across all subject areas. However, in order to ensure effective use of criteria, it is critical for teachers to develop an in-depth understanding of them. This paper reports on a study of a range of Australian Science teachers' views and uses of criteria in practical work. Six Science teachers working in secondary schools across Sydney were interviewed, their classroom activities were observed, and the data obtained were analysed using a qualitative constant comparative method. The findings indicate that despite the emphasis on Assessment for Learning (AfL) in assessment policy in Australia, teachers generally consider criteria as a marking tool, for Assessment of Learning (AoL), rather than a learning instrument. Consequently, they use criteria exclusively as a framework for assigning grades. This paper argues that teachers need to consider the use of criteria from a learning perspective in addition to its other multipurpose functions.