This paper explores a new approach to engage students in authoring educational content. This approach was implemented in AnnotEx (Example Annotator) system, which allows students to annotate computer programming examples with line-by-line explanations and review annotations produced by ther peers. A controlled study of AnnotEx presented in this paper evaluated the impact of the community peer-reviewing process on the quality of produced annotations and student learning. The study confirmed that

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... community feedback increases the volume and the quality of produced annotations and positively affects the work of weaker students. The peer-rating process enabled the community to distinguish good and bad annotations. Peer comments provided efficient guidelines for improving annotations and caused a significant increase in quality. Introduction and motivation Learning from examples is a common approach when mastering the art of computer programming. In this field, examples help students to master the semantics of programming language and to form problem-solving skills. Multiple code examples, ranging from small code snippets to complete programs, can be found in any programming textbook and are frequently also provided on an attached CD or a web site supporting the textbook. Researchers in the area of computer science education have also recognised the educational power of examples and have suggested a number of interactive systems, which have attempted to increase the value of examples as tools for learning (Brna