Two studies evaluated the effectiveness of a WWW-based formative assessment package used in undergraduate psychology courses. Students taking on-line multiple-choice tests received instant feedback on areas of weakness and how to address them. In Study 1, students used the package as an integral part of their course syllabus. Level of use correlated with performance in the end-of-course summative assessment. In Study 2, the package was used as an ‘optional extra’. Both studies found that students who used the package performed better than those who did not. Such systems may be useful learning tools which students may use to enhance performance.