Software modeling is a foundational skill in computer-science education, helping students visualize system structure, practice design principle, and reason about software architecture. UML is one of the most widely used tools for this purpose. However, the abstract nature of modeling concepts can make them challenging to grasp using traditional 2D tools. Immersive technologies such as virtual reality (VR) may offer more intuitive 3D representations that support comprehension and engagement. While prior research has explored the usability and motivational aspects of VR-based UML tools, few studies have directly compared learning outcomes between immersive and traditional environments. This study evaluates the effects of learning UML in VR versus a standard 2D desktop application, with a focus on both immediate and long-term retention. In our study, participants completed a baseline pretest, viewed a UML tutorial, and then took a post-test and a delayed final test two weeks later. Short-term learning outcomes were similar across conditions. However, VR participants scored significantly higher on the application-based diagramming question in the final test and reported greater confidence in their UML modeling abilities. These findings suggest that immersive environments may enhance retention and learner confidence in applied modeling tasks. Further research is needed to determine whether these benefits stem from the immersive qualities of VR or from differences in interface complexity.