Interactive computer-marked assessment has been incorporated into a range of science courses at the UK Open University. Different question types have been used, but all allow students multiple attempts so as to enable them to act on the feedback provided. An investigation is exploring the effectiveness of different question types and the impact of the way in which computer based assessment sits within the course's assessment strategy and whether it has summative, purely formative or diagnostic function. Qualitative and quantitative research methodologies include an analysis of data captured when students attempt the online questions. Characteristically different signatures of use have been identified for summative and purely formative interactive computer marked assignments. However there have been some surprises, indicating that student behaviour can be strongly influenced by their interpretation of advice given within a course and illustrating the need for further work in this are
