A variety of handheld applications and curricular materials have been developed to support inquiry science learning in recent years, but there are few handheld-supported assessment activities available to teachers. In Project WHIRL, researchers from SRI International worked in partnership with teachers from Beaufort County School District (SC) to develop a suite of handheld software applications that could be used to support classroom assessment in upper elementary and middle school science classrooms. In this paper, we will analyze results from a field trial conducted in 2003-2004 with 18 teachers in the district, focusing on how teachers' enactment of handheld-supported assessment activities altered the frequency and quality of their assessment practices.