While designing a database at the conceptual level using the Entity-Relationship (ER) model is challenging for novices, mapping an Entity-Relationship Diagram (ERD) to a relational schema is not an easy task, either. One of the problems is students’ lack of understanding of the underlying mapping principles. The mental gap between the two models in students also makes it difficult for them to perform the conversion. This paper describes two studies that aimed at helping students fill the gap and improve their ERD-Relational schema mapping performance by the use of a visualization tool, MySQL Workbench. We investigated the effect of using MySQL Workbench in teaching ERD-Relational schema mapping. We identified the pros and cons of using visualization in teaching the topic. Our results show that visualization can increase student interest and engagement, and facilitate students connecting the concepts in the two models. With an instructional delivery method that emphasizes the underlying mapping principles, a visualization tool could help undergraduate students improve their performance on ERD-relational schema mapping and facilitate their understanding of the ER model.