An important challenge faced by many teachers as they involve students in science investigations is measuring ("assessing") students' progress. Our detailed requirements analysis in a particular school district led to the idea that teachers need ways to improve the information they have about what students know and can do, not automation of typical assessment practices. We see handhelds as a promising for addressing this need because they can give students and teachers frequent, integral access to new ways of expressing and communicating what they know and can do.