This article contains a description of the organization and method of use of an active learning environment named MODeLeR, (Multimedia Object Design Learning Resource), a tool designed to facilitate the learning of concepts pertaining to object modeling with the Unified Modeling Language (UML). MODeLeR was created to provide an authentic, student-centered learning environment that embodies constructivist notions of learning. The context of this work is the study of object-oriented design in introductory and intermediate level programming classes where students typically do not have the opportunity to explore creation of large object-oriented systems or to perform collaborative work. The resource affords active, collaborative learning experiences in object oriented design with the goal of helping students to appreciate the need for design and to gain capability with UML. Students are required to create class diagrams, use-case diagrams and sequence diagrams. This article describes the MODeLeR environment, a method for its use, and a follow-on efficacy assessment from a pilot study (Coffey & Koonce, 2004). This article contains results of both a quantitative study and a qualitative evaluation of the resource. (Contains 3 figures and 4 tables.)