: Several studies have shown that explaining actions increases students’ knowledge. In this paper, we discuss how NORMIT supports self-explanation. NORMIT is a constraint-based tutor that teaches data normalization. We present the system first, and then discuss how it supports self-explanation. We hypothesized the self-explanation support in NORMIT would result in increased problem solving skills and better conceptual knowledge. An evaluation study of the system was performed, the results of which confirmed our hypothesis. Students who selfexplained learnt constraints significantly faster, and acquired more domain knowledge.