The Iterative Evaluation Model for Improving Online Educational Resources (IEM) was developed to provide a valid evaluation model to be used to improve online resources, to make them more effective and have a greater positive impact on student learning. The model focuses on the iterative evaluation of four components: (a) evaluation planning, (b) web design and content, (c) use of the educational resource, and (d) educational impact. This paper describes the IEM which was developed as part of the NSF-funded ARTIST (Assessment Resource Tools for Improving Statistical Thinking) project and used to evaluate the online resources developed by this project. The ARTIST evaluation is described in order to illustrate how the IEM may be used.