In previous work [10], we reported on an experiment performed in the context of SQL-Tutor, in which we analysed students’ self-assessment skills. This preliminary study revealed that more able students were better in assessing their knowledge. Here we report on a new study performed on the same system. This time, we analysed the effect of an open student model on students’ learning and self-assessment skills. Although we have not seen any significant difference in the post-test scores of the control and the experimental group, the less able students from the experimental group have scored significantly higher than the less able students from the control group. The more able students who had access to their models abandoned significantly less problems than the control group. These are encouraging results for a very simple open model used in the study, and we believe that a more elaborate model would be more effective.