The Diels-Alder reaction is one of the most well-known organic reactions and is widely used for six-membered ring formation. Regio- and stereo-selective Diels-Alder reactions have been emphasized in various areas including pharmaceutical and polymer industries. However, covering the theoretical background of such reactions in an undergraduate class is challenging because the interactions between molecular orbitals is poorly visualized for students. Especially when dealing with polycyclic aromatic hydrocarbons (PAHs) and asymmetric compounds, the complexity of regio- and stereo-selectivity becomes more pronounced. Herein we utilized web-based computational tools (WebMO) to visualize the HOMO-LUMO of each reaction component and their interaction to form chemical bonds. In this study we demonstrated the incorporation of computational aids into a Diels-Alder laboratory class dramatically facilitates students' understanding of several important concepts including frontier orbital theory, thermodynamics of the reaction, three-dimensional visualization, and so on. The assessment of teaching effectiveness prior to and after implementation of computational aids into Diels-Alder reactions will also be discussed in this manuscript.