The purposes of an online system to auto-mark students' responses to mathematics test items are to expedite the marking process, to enhance consistency in marking and to alleviate teacher assessment workload. We propose that a semi-automatic marking and customizable feedback system better serves pedagogical objectives than a fully automatic one. The two pedagogical objectives to be addressed are that teachers should know about the range of students' solutions and that they should provide meaningful feedback to students through the utilization of "customisable feedback". Both objectives are aligned with using assessment data for learning. Our proposed IT-based system consists of a marking component and a feedback component, and it is designed to provide close linkage between IT-based marking and these pedagogical objectives.