This paper presents our attempt to develop a personalized exam preparation tool for Java/OOP classes based on a fine-grained concept model of Java knowledge. Our goal was to explore two most popular student model-based approaches: open student modeling and problem sequencing. The result of our work is a Java exam preparation tool, KnowledgeZoom. The tool combines an open concept-level student model component, Knowledge Explorer and a concept based sequencing component, Knowledge Maximizer into a single interface. This paper presents both components of KnowledgeZoom, reports results of its evaluation, and discusses lessons learned.