In this paper we show how the deployment of a lightweight note sharing system can restore the antique social vocation of annotations in the classroom. The system was designed for the classroom context and evaluated through a longitudinal study lasting for an academic semester and involving 20 participants, enrolled in a Master-level course in computer science. Three key findings emerged. First, the tool spontaneously became an integral part of the classroom learning practices. Students took and shared annotations during the lectures and used them as complementary preparation material for the exam. Second, a correlation was observed between the annotation browsing time and the final exam grade. Third, a social bias emerged in favor of accessing one's own and friends' annotations. Based on the results, we discuss potential design implications for the system.